Skip to main content

Full text of "Planning scenario in Humboldt and Del Norte Counties, California for a great earthquake on the Cascadia subduction zone"

See other formats


Physica 
Sci .Lib 

QE 
89 
Al 
C32 
no. 115 




^QE8 

lC3 



.no. 115 
( Phys Sci 
Lib 



PLANNING 

HUMBOLDT AND DEL NORTE COUNTIES, CALIFORNIA 





THE RESOURCES AGENCY 

DOUGLAS P. WHEELER 
SECRETARY FOR RESOURCES 






STATE OF CALIFORNIA 

PETE WILSON 
GOVERNOR 



,__. .. ... .. 

DEPARTMENT OF CONSERVATION 





DIVISION OF MINES AND GEOLOGY 

JAMES F. DAVIS 
STATE GEOLOGIST 



Copyright © 1 995 by the California Department of Conserva- 
tion, Division of Mines and Geology. All rights reserved. No part 
of this publication may be reproduced without written consent 
of the Division of Mines and Geology. 



CALIFORNIA DEPARTMENT OF CONSERVATION 
DIVISION OF MINES AND GEOLOGY 



SPECIAL PUBLICATION 115 



PLANNING SCENARIO IN HUMBOLDT AND DEL NORTE COUNTIES, CALIFORNIA 
FOR A GREAT EARTHQUAKE ON THE CASCADIA SUBDUCTION ZONE 



By 

Tousson Toppozada, Glenn Borchardt, Wayne Haydon, 
and Mark Petersen 

California Department of Conservation 
Division of Mines and Geology 
801 K Street, MS 12-31 * 
Sacramento, California 95814-3531 



and 

Consultants 

Robert Olson, Henry Lagorio, and Theodore Anvik 



Tsunami inundation information provided by the National Oceanic 
and Atmospheric Administration 



Funded by the California Office of Emergency Services 
and the Federal Emergency Management Agency 



January 1995 



UNIVERSITY OF CALIFORNIA 
DAVIS 

MAY 3 1 1995 

CALIF. DEPOS. 
GOVT. DOCS. . LIBRARY 



Digitized by the Internet Archive 

in 2012 with funding from 

University of California, Davis Libraries 



http://archive.org/details/planningscenario115topp 






NORTH COAST SCENARIO 

TABLE OF CONTENTS 

Page 

INTRODUCTION 1 

EXECUTIVE SUMMARY 3 

PREVIOUS WORK 9 

ACKNOWLEDGMENTS 10 

SECTION 1. GEOLOGY AND SEISMOLOGY 13 

Earthquake Potential Along the Cascadia Subduction Zone 13 

Earthquake History of Humboldt and Del Norte Counties 16 

Paleoseismology 17 

Rationale for Selecting the Scenario Earthquake 17 

Characteristics of the Scenario Earthquake 18 

Tsunami Hazard 19 

Ground Motion and Intensity 22 

1 . Global Earthquake Analogy 22 

2. Instrumental Estimates 24 

Geologic Corrections 25 

Shaking Effects Predicted 26 

Ground Failure 27 

Fault Rupture 27 

The Alquist-Priolo Earthquake Fault Zoning Act 27 

Rupture Postulated for the Little Salmon Fault 28 

Liquefaction 28 

Crescent City 29 

Humboldt Bay 30 

Landslides 30 

1 . Known Landslides 31 

2. Potential Coherent Slides 31 

3. Potential Noncoherent Slides 31 

SECTION 2. BUILDINGS AND STRUCTURES 

BUILDINGS AND STRUCTURES 33 

Introduction 33 

Seismic Considerations 34 

Building Damage and Ground Motions 34 

Special Earthquake Hazard Mitigation Legislation in California 35 

The Field Act 35 

Hospital Act and Unreinforced Masonry Building Abatement Act 36 

Potentially Hazardous Buildings 36 

Unreinforced Masonry Buildings 36 

URM Buildings in the Study Area 37 

Pre-1 940 Wood Frame Houses 41 

Other Potentially Hazardous Structures 44 

Tsunamis and Buildings 46 

Planning Considerations 48 

Pelican Bay State Prison 49 

Planning Scenario 49 



NORTH COAST SCENARIO 

TABLE OF CONTENTS 

Page 

SECTION 2. BUILDING AND STRUCTURES (cont.) 

PUBLIC HIGH SCHOOLS AND COLLEGES 51 

General Characteristics 51 

Seismic Considerations 52 

Planning Considerations 54 

Planning Scenario 55 

HOSPITALS 57 

General Characteristics 57 

Seismic Considerations 57 

Planning Considerations 61 

Planning Scenario 61 

SECTION 3. TRANSPORTATION LIFELINES 

HIGHWAYS 63 

General Characteristics 63 

Seismic Considerations 63 

Planning Considerations 64 

Highways and Bridges 65 

Damage Assessments 66 

AIRPORTS 81 

General Characteristics 81 

Seismic Considerations 81 

Planning Considerations 83 

Planning Scenario 83 

Damage Assessments 83 

MARINE FACILITIES 89 

General Characteristics 89 

Seismic Considerations 89 

Planning Considerations 91 

Planning Scenario 91 

Damage Assessments 92 

RAILROADS 94 

General Characteristics 94 

Seismic Considerations 95 

Planning Considerations 96 

Planning Scenario 96 

Damage Assessments 97 

SECTION 4. UTILITY LIFELINES 

ELECTRIC POWER 101 

General Characteristics 101 

Seismic Considerations 103 

Planning Considerations 105 

Planning Scenario 106 

Damage Assessments 106 



NORTH COAST SCENARIO 

TABLE OF CONTENTS 

Page 

SECTION 4. UTILITY LIFELINES (cont.) 

NATURAL GAS 110 

General Characteristics 110 

Gas Field Operations 110 

Seismic Considerations 111 

Planning Considerations 113 

Planning Scenario 113 

Damage Assessments 114 

WATER SUPPLY FACILITIES 117 

General Characteristics 117 

Humboldt Bay Municipal Water District, Humboldt County 117 

Crescent City Water Supply District, Del Norte County 119 

Seismic Considerations 119 

Planning Considerations 1 22 

Planning Scenario 123 

Damage Assessments 1 24 

WASTE WATER 1 28 

General Characteristics 128 

Seismic Considerations 1 29 

Planning Considerations 131 

Planning Scenario 132 

Damage Assessments 133 

PETROLEUM PRODUCTS 1 35 

General Characteristics 135 

Historical Oil Field Operations 135 

Seismic Considerations . 135 

Planning Considerations 136 

Planning Scenario 137 

Damage Assessments 138 

GLOSSARY 140 

REFERENCES 142 



SECTION 5. APPENDIXES 

APPENDIX A: Modified Mercalli Scale 1 53 

APPENDIX B: Maps of Seismic Intensity and Lifelines 157 

APPENDIX C: Earthquake Fault Zone Maps for the 159 

Little Salmon Fault 



iii 



NORTH COAST SCENARIO 

TABLE OF CONTENTS 

Page 

SECTION 2. BUILDING AND STRUCTURES (cont.) 

PUBLIC HIGH SCHOOLS AND COLLEGES 51 

General Characteristics 51 

Seismic Considerations 52 

Planning Considerations 54 

Planning Scenario 55 

HOSPITALS 57 

General Characteristics 57 

Seismic Considerations 57 

Planning Considerations 61 

Planning Scenario 61 

SECTION 3. TRANSPORTATION LIFELINES 

HIGHWAYS 63 

General Characteristics 63 

Seismic Considerations 63 

Planning Considerations 64 

Highways and Bridges 65 

Damage Assessments 66 

AIRPORTS 81 

General Characteristics 81 

Seismic Considerations 81 

Planning Considerations 83 

Planning Scenario 83 

Damage Assessments 83 

MARINE FACILITIES 89 

General Characteristics 89 

Seismic Considerations 89 

Planning Considerations 91 

Planning Scenario 91 

Damage Assessments 92 

RAILROADS 94 

General Characteristics 94 

Seismic Considerations 95 

Planning Considerations 96 

Planning Scenario 96 

Damage Assessments 97 

SECTION 4. UTILITY LIFELINES 

ELECTRIC POWER 101 

General Characteristics 101 

Seismic Considerations 103 

Planning Considerations 105 

Planning Scenario 106 

Damage Assessments 106 



NORTH COAST SCENARIO 

TABLE OF CONTENTS 

Page 

SECTION 4. UTILITY LIFELINES (cont.) 

NATURAL GAS 110 

General Characteristics 110 

Gas Field Operations 110 

Seismic Considerations 111 

Planning Considerations 113 

Planning Scenario 113 

Damage Assessments 114 

WATER SUPPLY FACILITIES 117 

General Characteristics 117 

Humboldt Bay Municipal Water District, Humboldt County 117 

Crescent City Water Supply District, Del Norte County 119 

Seismic Considerations 119 

Planning Considerations 122 

Planning Scenario 123 

Damage Assessments 1 24 

WASTE WATER 1 28 

General Characteristics 128 

Seismic Considerations 129 

Planning Considerations 131 

Planning Scenario 132 

Damage Assessments 1 33 

PETROLEUM PRODUCTS 135 

General Characteristics 135 

Historical Oil Field Operations 135 

Seismic Considerations 135 

Planning Considerations 136 

Planning Scenario 1 37 

Damage Assessments 138 

GLOSSARY 140 

REFERENCES 142 



SECTION 5. APPENDIXES 

APPENDIX A: Modified Mercalli Scale 153 

APPENDIX B: Maps of Seismic Intensity and Lifelines 157 

APPENDIX C: Earthquake Fault Zone Maps for the 159 

Little Salmon Fault 



iii 



NORTH COAST SCENARIO 

TABLE OF CONTENTS 

Page 

TABLES 

Table S-1 Earthquakes of M>6% Causing Damage in Humboldt and/or Del Norte 17 

Counties 

Table S-2 Intensity-Distance Relations for Selected Shallow Earthquakes 23 

of Depth 1 to 30 km 

Table S-3 Geologic Units and Shaking Intensity Correction Factors 26 

Table B-1 Types of Damage to URM Buildings in the City of San Francisco 40 

After the 1 989 Loma Prieta Earthquake 

Table B-2 Damage to Private Buildings with Masonry Walls in Eureka 41 

After the 1 954 Earthquakes 

Table B-3 Significantly Damaged Wood Frame Dwellings in 1 969 Santa Rosa 43 

Earthquake 

Table PS-1 Public High Schools & Colleges Humboldt and Del Norte Counties 52 

Table H-1 Principal Hospitals in Humboldt and Del Norte Counties 58 

Table H-2 Northridge Earthquake - Initial Impact on Area Hospitals 60 

Table A-1 Commercial and Major Secondary Airports 82 

Table E-1 Principal Communities Served by Electric Power Companies 102 

Table E-2 Electric Generating Plants in the Planning Area 102 

Table W-1 Water Service Agencies and Sources of Supply 118 

Table WW-1 Major Treatment Facilities 129 

FIGURES 

Figure S-1 Simplified map of northwestern California regional tectonics 14 

Figure S-2 The Gorda segment of the Cascadia Subduction zone 16 

Figure S-3 Perspective map showing the extent of flooding in Crescent 21 

City from the 1964 Alaska earthquake tsunami. 

Figure B-1 Typical unreinforced masonry bearing wall building (URM) 37 

Figure B-2 Schematic distribution of URMs in Eureka 39 



iv 



NORTH COAST SCENARIO 
TABLE OF CONTENTS 

FIGURES (cont.) 



Page 



Figure B-3 Typical pre-1940 wood frame building 42 

Figure B-4 Typical pre-1973 tilt-up construction 45 

Figure B-5 Typical non-ductile concrete frame 46 

PHOTOS 

Photo B-1 Unreinforced brick buildings frequently lose parts of walls 38 

in earthquakes. 

Photo B-2 The front door was at the top of the stairs before this 43 

Ferndale house was shaken off its foundation. 

Photo B-3 Trailer home park in the village of King Salmon, south of 44 

Eureka. 

Photo B-4 This non-ductile concrete parking structure suffered severe 47 

damage and partially collapsed in the 1 987 Whittier earthquake. 

Photo B-5 Close-up of the parking structure showing structural failure of 47 

the non-ductile concrete columns. 

Photo H-1 Collapsed steel rebar and concrete columns of the Cypress 64 

I-880 freeway structure, Oakland, California. 

Photo H-2 The old bridge across the Eel River at Fernbridge 70 

Photo H-3 Route 101 Fields Landing Overhead 71 

Photo H-4 Route 1 99 between Cedar Springs and Washington Flat 79 

Photo R-1 Railroad bridge across South Fork Eel River at Scotia 98 

Photo R-2 Railroad tracks beneath Fields Landing overpass 98 

Photo E-1 Humboldt Bay Power Plant, cooling water channel, and substation 108 

Photo W-1 Matthews Dam and Ruth Lake 118 



NORTH COAST SCENARIO 

INTRODUCTION 

This report assesses the vulnerability of lifelines in northwestern California to a major earthquake 
on the Cascadia Subduction Zone (CSZ). The planning area, consisting of Humboldt and Del Norte 
counties, is about 50 miles (80 km) east to west and 140 miles (225 km) north to south. The area 
includes Eureka, Areata, Crescent City, and many smaller communities. Over 1 50,000 people 
reside in the planning area, 1 27,000 in Humboldt County, and 29,000 in Del Norte County 
(Population Estimates, State of California, Department of Finance, 1.1.94, Report 94 E-1). 

The regional geologic and seismologic basis for development of the scenario damage assessments 
includes the earthquake shaking intensities, the areas with potential for liquefaction, the areas 
subject to seismically induced landslides, and the generation of a seismic sea wave or tsunami. 
This information enables the reader to visualize the potential vulnerability of lifeline facilities. 

The damage assessments illustrate a regional damage pattern that can result from an earthquake of 
magnitude (M) 8.4 on the Gorda segment of the CSZ. An earthquake of different magnitude or 
location on this fault, or an event on any of the other faults in the planning area, would result in 
different intensity and damage patterns. 

The seismic intensity distribution from which the damage is assessed, is based on a particular 
model. There is no general agreement as to the most realistic model to be used for predicting 
intensity distribution, and a different model would yield a different intensity pattern. In addition, 
the quality of available information on which the seismic intensity distribution map is based varies 
throughout the planning area. Only general geologic information is available for most of the area. 
Modeling of ground shaking on a regional basis using this generalized geologic information produces 
plausible conclusions appropriate only for emergency planning. Conclusions regarding specific 
structures, such as the desirability of upgrading seismic resistance, require detailed engineering 
analysis and site-specific geologic information which are beyond the scope of this planning 
scenario. Likewise, the tsunami flooding scenario is based on an approximate model and is not site 
specific or accurate in detail. 

While no planning scenario can be accurate in detail, it provides planners with a regional pattern of 
the types of problems that will confront emergency response personnel. 



NORTH COAST SCENARIO 

This planning scenario is intended to contribute to the efforts of the following users: 

• Local, state, and federal officials with emergency planning responsibilities. 

• Elected officials who need to visualize the threat in order to commit themselves to 
leadership in mitigating the hazard and planning for response. 

• Private sector managers and planners who must understand the scope of the hazard to 
prepare for it. 

• Educators, journalists, and others who must communicate to the public the character of 
the threat, and the importance of preparedness in mitigating its effects. 

• The general public who need to support public mitigation efforts and develop personal 
strategies to minimize the effects of the earthquake on themselves and their families. 



NORTH COAST SCENARIO 



EXECUTIVE SUMMARY 

The Cascadia Subduction Zone (CSZ) Gorda Segment 

The CSZ is a 750 mile (1,200 km) long offshore major thrust fault zone extending from northern 
California to southern Canada. This planning scenario hypothesizes a M8.4 (moment magnitude) 
earthquake on the southernmost 1 50 mile (240 km) Gorda segment of the CSZ. This may not be 
the largest event that could occur along the CSZ, but it will produce within California about as 
much destruction as would a rupture of the entire zone. The probability of occurrence of the 
scenario earthquake is not known, but is sufficient to justify preparedness planning. 

The Scenario Earthquake 

The scenario earthquake is based on the following characteristics: 

1 . The Gorda segment of the CSZ, extending 1 50 miles (240 km) from Cape Mendocino to 
Cape Blanco ruptures in an earthquake of M8.4. 

2. The ocean floor undergoes a maximum surface displacement of 26 feet (8 m), with the 
east side up, on a fault dipping 1 1 degrees to the east beneath Humboldt and Del Norte 
counties. 

3. Sea floor deformation generates a destructive sea wave or tsunami. 

4. Triggered offset along the Little Salmon fault averages 6 feet (2 m). 

5. Potentially damaging ground shaking continues for about 60 seconds within 25 miles 
(40 km) of the fault. Humboldt and Del Norte counties are less than 25 miles above the 
CSZ fault plane which dips gently eastward, and are wholly within the zone of damaging 
shaking. 

6. Potentially damaging aftershocks occur for several months following the main shock, with 
a few earthquakes in the M6 to M7 range. 

Shaking Effects 

Shaking intensities are generally greatest near the coast and decrease inland. This pattern is 
modified by the areal distribution of geologic materials that vary in their response to shaking. 
Overall, the intensities are high because the fault plane is directly beneath most of the coast at 
depths of 6 to 12 miles (10 to 20 km). 

For alluvial sites, the Modified Mercalli Intensity (MMI) IX zone (MMI is described in Appendix A) 
extends inland from the coast about 45 miles (70 km) in southern Humboldt County, and about 
6 miles (10 km) in northern Del Norte County. 



NORTH COAST SCENARIO 

The MMI VIII + areas often surround the MMI IX areas, and cover the hills above Humboldt Bay and 
the Eel River Plain. Most of the three main population centers of the study area, Eureka, Areata, 
and Crescent City, are in the MMI VIII + area. 

Local intensities could be greater than those from shaking only, mainly due liquefaction in alluvial 
areas, and landslides in hilly areas. 

Tsunami 

The scenario earthquake is assumed to generate a local seismic sea wave or tsunami that will arrive 
just minutes after the earthquake occurs. The lack of warning time from such a nearby event will 
result in higher casualties than if it were a distant tsunami source wherein the Tsunami Warning 
System for the Pacific Ocean could warn threatened coast areas in time for evacuation. In low 
lying coastal areas, strong shaking should be taken as a warning of a potential tsunami, and 
individuals should immediately move to higher ground. The tsunami model for this scenario was 
provided by the National Oceanic and Atmospheric Administration (Bernard and others, 1994). 

In Humboldt County the greatest impact on populated areas will be the inundation of the Samoa 
Peninsula, and to a lesser degree the village of King Salmon, which faces the opening of Humboldt 
Bay (Map S-1). Earthquake damage to Highway 255 across the bay to Eureka and northward to 
Areata will compound the tsunami problem by isolating the Samoa Peninsula. A possible refuge 
from the tsunami might be afforded by a 1.5 mile-long by 300-foot- wide ridge of wooded dunes of 
elevation 40 to 70 feet just west of Manila, 2 miles north of Samoa, and 4 miles north of 
Fairhaven. The tsunami impact on the village of King Salmon and the PG&E power plant will be 
less severe than on the Samoa Peninsula, but will compound the damage from intense ground 
shaking (MMI IX) and liquefaction. Humboldt and Areata bays will be choked with debris from the 
Samoa Peninsula. 

At Crescent City the tsunami destruction will exceed that which occurred from the 1 964 Alaska 
tsunami. The 1 964 run-up reached 4th Street, while this scenario postulates tsunami run-up 
reaching 8th Street. Crescent City experienced ten fatalities and over $7 million in damage from 
the tsunami caused by the M9.2 Alaska earthquake of 1964. 

Damage Assessments 

Damage assessments have been postulated for certain lifeline facilities. The statements regarding 
the performance of facilities are intended for planning purposes only, and are not site-specific 
engineering evaluations. 



NORTH COAST SCENARIO 

The scenario addresses primarily the initial 3 day response period. After 3 days, repairs and 
response will be dictated by the observed post-earthquake situation. The out of service times 
indicated below assume that equipment, repair materials, access to the damage site, and response 
personnel are available. If they are not concurrently available for all lifelines, then priorities must be 
set, and certain lifeline elements will be out of service for longer periods. 

Schools and Colleges 

The high schools and colleges will experience MMI VIII + or IX ground shaking resulting in major 
nonstructural and some structural damage. Because of their size, location, and service facilities, 
public schools, and in particular high school buildings, are desirable as evacuation shelters and 
mass feeding centers. 

For planning purposes, it is assumed that underground utility service lines such as water, natural 
gas, and sewage will be ruptured in soft ground areas. As a result, some schools will have 
functional impairments even if they remain structurally safe. 

Humboldt State University, one of the system's older campuses, is located slightly north of Areata 
and contains numerous buildings, varying greatly in age, type of construction, size, and occupancy. 
Some earthquake rehabilitation projects have been undertaken on the campus and others are yet to 
be completed. 

The College of the Redwoods is new enough to have been built under the requirements of the Field 
Act, and no significant structural damage is expected from shaking. However, significant damage 
will occur because it is adjacent to the Little Salmon fault which will rupture in this scenario. Also, 
transportation and utility services will be interrupted where such systems traverse the fault. 

Hospitals 

While there are five hospitals in the main impact area, they have a total of only 348 beds. For 
response planning purposes, we anticipate that 119 (34 percent) will be unavailable for treatment 
of earthquake related casualties. This limited capacity plus the possibilities of damage, loss of 
utility services, disruption of roads, and the long distance to any other comparable facility, means 
that some of the most seriously injured may have to be evacuated by air to hospitals outside 
Humboldt and Del Norte counties. 

Highways 

Highway 101 will be unusable in most of Humboldt and Del Norte counties for at least the 3 day 

duration of this scenario and for up to a month later. The bridge between Eureka and the Samoa 



5 



NORTH COAST SCENARIO 

Peninsula will also be unusable. Likewise easterly routes through the mountains (e.g. Routes 36, 
299, 96, and 1 99) will be blocked by landslides and other damage. Planners need to identify 
access routes to communication centers, hospitals, airports, staging areas, fuel storage sites, and 
other locations necessary for emergency response. Highway outages will restrict emergency 
supplies from outside the area for 14 days. 

Airports 

Emergency air transport to and from the disaster area is vital to response activities, particularly 
during the first 3 days. The best options under the scenario conditions will be Arcata-Eureka 
Airport and McNamara Field in Crescent City, both of which can handle C-130 transport aircraft. 
The other small outlying airports in the planning area might be useable for small fixed wing and 
helicopter aircraft. They could be used to evacuate casualties and bring in key personnel and 
supplies. However, the condition of each would have to be determined before they are used as 
some may be damaged, require portable communications and air traffic control equipment, or be 
inaccessible due to damage to the connecting roads. Local emergency officials should consider 
these problems, by referring to the damage assessments listed in the Airports chapter. 

Marine Facilities 

Most of the docks in Eureka are supported on piles and are not expected to suffer severe damage 
from shaking. Tarmacs, aprons, access roads, and other paved surfaces placed over fill areas will 
fail due to settlement and spreading of soils owing to liquefaction induced by strong ground 
shaking. Humboldt/Arcata Bay is partially protected from tsunami damage by the Samoa Peninsula 
and South Spit. We expect the peninsula to be overtopped, and structures and lifelines there to be 
severely damaged. At Eureka harbor, debris from the tsunami and hazardous material spills will add 
to the earthquake damage. 

In Crescent City severe damage to docks and other structures will be comparable to that 
experienced in the 1964 tsunami, causing loss of function for an extended period. 

Railroads 

The rail lines along the Eel River, Humboldt Bay, and Areata Bay, will be disrupted by liquefaction 
and landslides and closed for repairs for several weeks. All movable span bridges in MMI VIII + to 
IX zones are subject to misalignment due to heavy ground shaking. In general, we expect that 
many of the older bridges will be closed along the North Coast Railroad's right of Way. 



NORTH COAST SCENARIO 

Electric Power 

During the first 3 days after the earthquake the entire planning area will experience some loss of 
power, at least temporarily. The cities of Fortuna, Eureka, Areata, and Crescent City are in 
strongly shaken areas (MMI VIII + and IX) and will experience significant power outages. Service 
to most areas will be restored in 24 hours, but some parts of the cities and rural areas may 
experience outages lasting as long as 5 days. 

The private power plants at Samoa and Fairhaven will be severely damaged by the tsunami. The 
PG&E power plant at King Salmon will be damaged by the earthquake more than by the tsunami. 

Natural Gas 

Sources of natural gas and propane that are outside the strongly shaken areas are not expected to 
be damaged or impaired by the scenario earthquake. Humboldt County is supplied by gas from 
Sacramento Valley and from Tompkins Hill gas field. Both transmission lines will be damaged 
where they cross the Little Salmon fault. 

Numerous breaks and leaks will occur in service to mains connections and in the local distribution 
system throughout the strongly shaken area, especially wherever ground failure occurs as a result 
of liquefaction. Fires will break out in the downtown areas of Eureka, particularly where older 
wood frame buildings are clustered in areas of potential liquefaction. Local fires caused by gas 
appliance connections and in gas pipelines will occur in mobile home parks and other communities, 
particularly those experiencing MMI VIII or greater shaking. 

The damage to water supply services will make firefighting difficult in these areas. Unless 
emergency water supply is immediately available, fire control could take from 48 to 72 hours. 

Petroleum Products 

Tanks bordering Humboldt Bay in Eureka will buckle and leak due to MMI IX shaking and 
liquefaction effects. Tanks in Crescent City will be destroyed by the tsunami, resulting in 
hazardous spills and fires. Given the area's dependence on imported supplies, and the vulnerability 
of Highway 101 and the local tank facilities, there will be a shortage of gasoline in the area. 

Water SuddIv 

The water supply from Humboldt Bay Water District intakes along the Mad River, and the Crescent 
City Water District intake along the Smith River will be reduced due to power outages and to 
transmission line breaks caused by liquefaction ground failures. There will be breaks in the 



NORTH COAST SCENARIO 

distribution pipelines in residential areas. Localized fires will occur in some urban areas, and will be 
difficult to fight unless emergency water supplies are immediately available. 

Waste Water 

Soil liquefaction will be a major source of damage to treatment plants and to sewage lines. 
Untreated sewage will bypass damaged treatment plants and will be dumped into holding ponds, 
creeks, rivers, bays, or the ocean. The tsunami will damage treatment plants and outfall lines in 
Crescent City, Areata, and Eureka. 



NORTH COAST SCENARIO 

PREVIOUS WORK 
By the California Division of Mines and Geology 

The Governor's Emergency Task Force on Earthquake Preparedness was established in February 
1981. Some 30 committees were formed to deal with improvement of the many emergency 
response functions that would be needed in an earthquake emergency: communications, search 
and rescue, fire services, medical services, air transport, etc. A Threat Assessment Committee 
was also created to characterize the consequences of credible earthquakes as a basis for these 
emergency response planning efforts. Working with the Task Force, the Department of 
Conservation, Division of Mines and Geology developed two earthquake planning scenarios (Davis 
and others, 1982a, 1982b). These scenarios were based on a repeat of the 1906 San Francisco 
earthquake (M~8) on the northern San Andreas fault and a repeat of the 1857 Fort Tejon 
earthquake (M~8) on the south-central San Andreas fault. 

With support from the National Earthquake Hazards Reduction program the Division of Mines and 
Geology also developed planning scenarios for the Hayward fault (Steinbrugge and others, 1 987), 
and the Newport-lnglewood fault zone (Toppozada and others, 1988); with support from the 
Governor's Office of Emergency Services and the Federal Emergency Management Agency for the 
San Diego-Tijuana area (Reichle and others, 1 990), the Riverside-San Bernardino area (Toppozada 
and others, 1993), and the northern San Francisco Bay area (Toppozada and others, 1994). 



NORTH COAST SCENARIO 

ACKNOWLEDGMENTS 

This study was funded by the Governor's Office of Emergency Services (OES), and the Federal 
Emergency Management Agency. Richard Eisner and Edward Bortugno, both of OES, provided 
helpful review and comments. 

We thank the many individuals with whom we met for informative discussions and field inspections 
of various critical facilities, and those who reviewed or otherwise participated in the preparation of 
this report. 

The cooperation and assistance of the staff of the various utilities and agencies that we contacted 
is gratefully acknowledged. The informative discussions and opportunities to visit facilities were 
invaluable. Critical reviews of the different chapters by experts in the field greatly improved the 
quality and credibility of this report. 



Dr. Eddie Bernard (NOAA) provided the tsunami model and reviewed our tsunami hazard 
assessments. 

Drs. Samuel Clarke (USGS), Michael Reichle (DMG), and Kenji Satake (Univ. of Michigan), 
provided the input to determine fault parameters. Dr. Reichle also provided advice on the 
ground motion model. 

Dr. Jack Evernden (USGS) provided critical discussion and input of the ground motion 
determination, and ran his model for a line source beneath Eureka for testing purposes. 

Drs. Gary Carver and Lori Dengler (Humboldt State University) provided critical input on the 
local geology, and advice throughout the study. 

Dr. Woody Savage (PG&E) provided information and review for the chapters on Electric Power 
and Natural Gas. 

Ann Gilbert-Sardo (Caltrans) provided input and review for the Highways chapter. 

Gary Boughton (Assistant City Engineer, Eureka), provided information on the petroleum and 
water tanks in Eureka. 

Jan Ware (Anvick Engineering), Ken Olson (VSP Associates), and Benjamin Chuaqi 
(UC Berkeley) assisted with gathering field information. 

Jack McMillan (DMG) provided input and review for lifeline vulnerabilities in Eureka and 
Crescent City. 

Robert Moskovitz (DMG) assisted with computing the distances from the surface to the 
dipping fault plane. 



10 



NORTH COAST SCENARIO 

Ted Smith (DMG) reviewed the Geology and Seismology Chapter. 

Claudia Hallstrom critically proofed and assembled the report. 

Marialena Tabillo provided expert editing. 

We are grateful to Joy Sullivan, Jim Williams, and Ross Martin for drafting the maps and to 
Jeffrey Tambert for supervising the publication. 

Finally, we thank Virginia Williams, who cheerfully and skillfully transformed myriad drafts, 
notes, revisions, and additions into this final report. 



11 



GEOLOGY AND SEISMOLOGY 



SCENARIO MAPS AND DAMAGE ASSESSMENTS 

ARE INTENDED FOR EMERGENCY PLANNING 

PURPOSES ONLY 



THEY ARE BASED ON THE FOLLOWING HYPOTHETICAL 
CHAIN OF EVENTS: 

1 . A PARTICULAR EARTHQUAKE OCCURS 

2. VARIOUS LOCALITIES IN THE PLANNING AREA 
EXPERIENCE A SPECIFIC TYPE OF SHAKING OR 
GROUND FAILURE 

3. CERTAIN CRITICAL FACILITIES UNDERGO DAMAGE AND 
OTHERS DO NOT 

THE CONCLUSIONS REGARDING THE PERFORMANCE OF 
FACILITIES ARE HYPOTHETICAL AND AND NOT TO BE 
CONSTRUED AS SITE-SPECIFIC ENGINEERING EVALUATIONS. 
FOR THE MOST PART, DAMAGE ASSESSMENTS ARE STRONGLY 
INFLUENCED BY THE SEISMIC INTENSITY DISTRIBUTION MAP 
DEVELOPED FOR THIS PARTICULAR SCENARIO EARTHQUAKE. 
THERE IS DISAGREEMENT AMONG INVESTIGATORS AS TO 
THE MOST REALISTIC MODEL FOR PREDICTING SEISMIC 
INTENSITY DISTRIBUTION. NONE HAVE BEEN FULLY TESTED 
AND EACH WOULD YIELD A DIFFERENT EARTHQUAKE 
PLANNING SCENARIO. FACILITIES THAT ARE PARTICULARLY 
SENSITIVE TO EMERGENCY RESPONSE WILL REQUIRE A 
DETAILED GEOTECHNICAL STUDY. 

THE DAMAGE ASSESSMENTS ARE BASED ON THIS SPECIFIC 
SCENARIO. AN EARTHQUAKE OF SIGNIFICANTLY DIFFERENT 
MAGNITUDE ON THIS OR ANY ONE OF MANY OTHER FAULTS 
IN THE PLANNING AREA WILL RESULT IN A MARKEDLY 
DIFFERENT PATTERN OF DAMAGE. 



NORTH COAST SCENARIO 

GEOLOGY AND SEISMOLOGY 

This chapter outlines the geologic and seismologic input used to model the scenario earthquake, and 
to develop the map showing the shaking intensities and the areas susceptible to liquefaction and 
landslides. The generation of a local seismic sea wave, or tsunami, is also discussed. 

We use seismic intensity, the earthquake effects on buildings, furnishings, etc. at a particular 
location, to evaluate damage. Intensity generally decreases with distance from the causative 
earthquake fault. Several intensity scales have appeared during the last century (Barosh, 1969). 
The Modified Mercalli Intensity (MMI) scale, used in this scenario, is reproduced in Appendix A. 

Earthquake magnitude is an instrumental measure of earthquake size, regardless of location or 
intensity effects. Magnitude does not decrease with distance from the causative fault, because its 
calculation compensates for distance. Earthquakes of similar magnitudes can have different 
reported intensities because of population distribution and ground conditions. For example, the 
1992 Landers earthquake (M7.5) had a maximum reported MMI of VIII, while the smaller 1994 
Northridge earthquake (M6.7) had a larger maximum reported MMI of IX, because it occurred within 
a densely populated area. 

The degree of ground shaking resulting from the scenario earthquake will depend on several factors. 
Among the most important is the distance from the fault plane and the site geology. Shaking 
generally diminishes with distance, and soft sediment can amplify ground motion increasing the 
potential for damage. 

Earthquake Potential Along the Cascadia Subduction Zone (CSZ) 

The CSZ is a 750 mile (1,200 km) long thrust fault extending offshore from northern California to 
southern Canada, and dipping gently eastward beneath North America (Figure S-1). On the south 
end, the CSZ intersects both the Mendocino fault and the San Andreas fault at the Mendocino triple 
junction. To the north, the fault zone intersects the Queen Charlotte fault, off the shore of British 
Columbia. The CSZ contains several plate segments that are subducting or thrusting beneath North 
America, as shown in Figure S-1 . The southernmost segment is the 1 50 mile (240 km) long Gorda 
plate, which extends from Cape Mendocino to southernmost Oregon. 

Geophysical measurements of the rocks on the sea floor indicate that the Juan de Fuca plate is 

being subducted or thrust beneath the North American plate along the CSZ at a rate of 

1 .6 inches/year (40 mm/yr) (Nishimura and others, 1984). Even though this movement or slip rate 



13 



NORTH COAST SCENARIO 




Figure S-1 Simplified map of northwestern California regional tectonics. To the south of the Mendocino triple 
junction (MTJ), the San Andreas fault system (SAF) is the transform (strike-slip) boundary 
between the Pacific and North American plates. North of Cape Mendocino (CM), the Juan de Fuca 
and Gorda plates are converging with the North American plate along the Cascadia subduction 
zone. West of Cape Mendocino, the Mendocino fault (MF) is the transform boundary between the 
Pacific plate and the Gorda plate. White arrows denote plate motion relative to North America; 
black arrows denote relative plate motion at plate boundaries. The inset is a simplified cross 
section of the southern Gorda plate being subducted beneath the North American plate in northern 
California. Reproduced from Dengler and others, 1992. 

is comparable to the slip rate for the San Andreas fault in central California, the CSZ has 
generated no great earthquakes (M>8) and very few large earthquakes (M>6) during the 150 years 
of recorded history (Heaton and Kanamori, 1 984; Heaton and Hartzell, 1 987; Dengler and others, 
1992). The 1992 Petrolia earthquake (M7) is the largest modern event associated with the CSZ 
(Oppenheimer and others, 1993). 

Recent geodetic data indicate northeast convergence near the plate interface. Geologic 
investigations near the south end of the CSZ indicate a rapid 0.14 inch/yr (3.6 mm/yr) tectonic uplift 
along the coast, and that at least nine emergent terraces and beach ridges were formed during the 



14 



NORTH COAST SCENARIO 

past 5,000 years (Lajoie, 1983). For these nine terraces to form, the uplift (3.6 mm/yr x 5000 yr = 
18 m) must have been episodic rather than gradual. It is possible they were created by nine large 
earthquakes occurring on average once every 500 years. The uplift of about 3 feet (1 m) produced 
during the M7 Petrolia event over a 6 mile (10 km) segment of the coast (Jayko and others, 1992; 
Stein and others, 1993) is significant in this regard. 

Heaton and Kanamori (1984) observed that the CSZ shares many characteristics with other global 
subduction zones that have generated great earthquakes (e.g., southern Chile). Like the CSZ, these 
zones have young crust, shallow dips, weak gravity anomalies, and subdued trenches. Thus, by 
analogy, we expect that the CSZ could also rupture in a great earthquake. 

The Gorda segment of the CSZ is composed of several fault strands that trend nearly 
north-northwest to south-southeast along most of the zone, changing to nearly east-west near 
Petrolia and the triple junction (Greene and Kennedy, 1989). The exact location of the southern 
boundary of the CSZ is not well established near the Mendocino triple junction. Although gravity 
and seismicity data have been interpreted as evidence that the CSZ extends southeast of Punta 
Gorda (Jachens and Griscom, 1 983; Castillo and Ellsworth, 1 993), other seismicity data and the 
1 992 aftershock pattern suggest that the seismogenic zone trends nearly due east of Punta Gorda 
(Smith and others, 1993; Oppenheimer and others, 1993). For this scenario we assume that the 
subduction zone extends southeast of Punta Gorda. 

Little is known about the possible independent seismic activity of the Gorda segment of the CSZ. 
Offshore reflection and refraction data indicate that the CSZ crops out some 40 miles (60 km) west 
of Eureka in water 1.5 miles (2.5 km) deep (Greene and Kennedy, 1989). Clarke (1992) indicates 
that the earthquake-producing or seismogenic portion of the subducting plate may be distinguished 
by faults and folded sediments in the overriding plate that trend nearly normal to the direction of 
plate convergence. The seismogenic zone may also be distinguished by seismicity having 
compressional mechanisms. He suggests that the interface dips easterly at about 1 1 degrees, and 
that the seismogenic zone extends from about 1 2 miles (20 km) eastward of the surface trace of 
the CSZ at a depth of 5 miles (8 km) for about 50 miles (80 km), to a depth of about 14 miles 
(23 km), as indicated in Figure S-2. 



15 



NORTH COAST SCENARIO 



Okm 



MOF7C 




MENDOCINO 



Juncture with 
San Andreas Fault 



42N° 



41N° 



125° 



124° 



40N° 



Figure S-2 The Gorda segment of the Cascadia Subduction zone (CSZ). The southern terminus is at the triple 
junction where it meets the Mendocino fault and the San Andreas, near the epicenter (star) of the 
1 992 Petrolia earthquake. The CSZ dips gently beneath Humboldt and Del Norte counties. It 
surfaces in the ocean bottom, indicated by km. The earthquake-producing portion is between 
depths of 8 km and 23 km. 

Earthquake History of Humboldt and Del Norte Counties 

The April 25. 1992 Petrolia earthquake (M7) occurred along the CSZ and is a reminder of the 
potential for even larger events on this zone (Oppenheimer and others, 1993). This earthquake 
occurred at about 6 miles (10 km) depth and its aftershocks extended about 14 miles (22 km) 
north-south and 20 miles (32 km) east-west along a zone dipping shallowly to the east. The 
earthquake generated a small tsunami that arrived after the earthquake by 20 minutes at Eureka, 
and by 47 minutes at Crescent City. Waves continued to arrive for 1 hours, and the strongest 
wave (1.5 feet or 53 cm) arrived at Crescent City almost 4 hours after the earthquake (Oppenheimer 
and others, 1993; Gonzalez and Bernard, 1992). Damaging aftershocks of M6.6 and M6.7 occurred 
about 1 Vi and 5 hours after and 20 miles (30 km) west of the mainshock. They occurred beneath 
the CSZ, at a depth of 12 miles (20 km) on a strike-slip fault (Oppenheimer and others, 1992). 

Earthquakes of M>6V4 that have caused damage (MMI>VI) in the planning area are listed in 
Table S-1, from the compilation of Dengler and others (1992). 



16 



NORTH COAST SCENARIO 



TABLE S-1 
EARTHQUAKES OF M>6V4 CAUSING DAMAGE IN HUMBOLDT AND/OR DEL NORTE COUNTIES 



DATE 


MAGNITUDE 


MMI 


LOCATION 


REFERENCE 


1873 November 22 


6 3/4 


VIII 


Del Norte Co. 


Toppozada & others, 1981 


1 906 April 1 8 


8 


VIII-IX 


Mendocino Co. -Santa Cruz Co. 


Toppozada & Parke, 1982 


1 909 October 28 


6% 


VIII 


Cape Mendocino area 


Toppozada & Parke, 1982 


1922 January 31 


7Y, 


VI 


60 km west of Areata 


Smith & Knapp, 1 980 


1923 January 22 


7 


VIII 


Off Cape Mendocino 


Smith & Knapp, 1980 


1932 June 6 


6X 


VIII 


30 km W of Eureka 


Toppozada & Parke, 1982 


1941 October 3 


6 V, 


VII 


40 km WNW of Cape Mendocino 


Smith & Knapp, 1980 


1954 December 21 


6!4 


VIII 


20 km NE of Areata 


TERA, 1977 


1980 November 8 


7 


VII 


50 km W of Trinidad 


Berkeley Seism. Station 


1992 April 25 


7 


VIII 


Petrolia 


Oppenheimer & others, 1993 


1994 September 1 


7 


VI 


1 40 km west of Petrolia 


Dengler & others, 1995 


1994 December 26 


5.4 


VI 


1 6 km west of Eureka 







Paleoseismoloqy 

Since 1986, paleoseismic evidence has been accumulating for either a single large event (M9.5) or a 
series of smaller events (M8.4) having occurred along the CSZ about 300 years ago (Atwater, 
1986, 1987, 1992; Atwater and Grant 1986; Carver and Burke, 1986, 1987a, 1987b, 1989, 
1 992; Burke and Carver, 1 992; Clarke and Carver, 1 992; Darienzo and Peterson, 1 990; Grant and 
Minor, 1991). Current knowledge indicates that such events have a recurrence interval of 300 to 
600 years {Wuethrich, 1994). 

Geologic trench investigations near Eureka reveal that movement on the Little Salmon and similar 
faults may have occurred at the same time as the CSZ earthquakes (Carver and Burke, 1987a, 
1987b, 1989, 1992). 

Rationale for Selecting the Scenario Earthquake 



The rationale for selecting the scenario earthquake is as follows: 

1 . Easterly movement of the Juan de Fuca at 1 .6 inches/year (40 mm/yr) and Gorda plates 
beneath the North American plate continues to build strain that could be released in great 
earthquakes. 

2. Coastal Humboldt and Del Norte counties are 6 to 12 miles (10 to 20 km) above the 
shallowly dipping CSZ. 

17 



NORTH COAST SCENARIO 



3. Paleoseismic evidence suggests that large or great tsunami-generating earthquakes occur 
every 300 to 600 years along the CSZ in northern California. 

4. CSZ earthquakes appear to be accompanied by movement on related land-based structures 
such as the Little Salmon fault. 

5. The liquefaction, landsliding, strong ground shaking, and large local tsunami likely to be 
associated with the scenario event are hazards that can be mitigated through proper 
planning. 



Characteristics of the Scenario Earthquake 

This planning scenario assumes rupture of the 1 50 mile (240 km) Gorda segment of the CSZ (Figure 
S-2). Although this may not be the largest event that could occur along the CSZ, it would produce 
within California about as much destruction as a rupure of the entire zone. 

Several empirical relations relate rupture length to average displacement for thrust earthquakes (e.g., 
Wyss, 1979; Scholz, 1982; Slemmons and Depolo 1986). From these relations, the average 
displacement predicted for the 240-km-long scenario rupture is between 1 6 and 26 feet (5 and 
8 m). The displacement along the fault surface and the area of rupture determine the size of the 
earthquake. By using an average displacement of 8 m, and the plate rupture dimensions of 240 km 
length, and 80 km width (Clarke and Carver, 1 992) we obtain a moment magnitude of 8.4. 

The 1 992 Petrolia earthquake is reported to have occurred on the CSZ. Oppenheimer and others 
(1993) indicate that the source of the 1992 Petrolia mainshock dipped about 13 degrees east, 
similar to previous interpretations of 1 to 1 5 degree dip from the seismicity along the CSZ (Smith 
and others, 1993; Clarke, 1992; Heaton and Kanamori, 1984, and Cockerham, 1984). For the 
scenario earthquake we use a rupture plane with a dip of 1 1 degrees and assume that the CSZ is at 
a depth of 6 miles (10 km) beneath the Petrolia earthquake epicenter, as indicated by Oppenheimer 
and others (1993). 

Based on paleoseismic studies, the Little Salmon fault appears to generate 10 to 15 feet (3.5 to 
4.5 m) of sympathetic coseismic slip during great CSZ earthquakes (Clarke and Carver, 1992). 
Therefore, we assume that the offset along the Little Salmon fault will be 1 2 feet (4 m) with the 
more prevalent average displacement at the ground surface being half the maximum value, or about 
6 feet (2 m). The displacement is such that the northeast side of the fault is thrust over the 
southwest side along a plane dipping 1 5 degrees to the northeast. This will produce about 3 feet 
(1 m) of relative vertical movement along the Little Salmon fault, distributed across a deformed zone 
tens of feet wide. 



18 



NORTH COAST SCENARIO 

We assume that potentially damaging ground shaking will continue for about 60 seconds within 25 
miles (40 km) of the fault. Humboldt and Del Norte counties are less than 25 miles above the CSZ 
fault plane which dips gently eastward, and are wholly within the zone of damaging shaking. 
Potentially damaging aftershocks could occur for several months following the main shock, with a 
few earthquakes in the M6 to M7 range. 

In summary, the scenario earthquake is based on the following characteristics: 

1 . The Gorda segment of the CSZ, extending 1 50 miles (240 km) from Cape Mendocino to 
Cape Blanco ruptures in an earthquake of M8.4. 

2. The ocean floor undergoes a maximum surface displacement of 26 feet (8 m), with the 
east side up, on a fault dipping 1 1 degrees to the east, beneath Humboldt and Del Norte 
counties. 

3. Sea floor deformation generates a destructive sea wave or tsunami. 

4. The triggered offset along the Little Salmon fault averages 6 feet (2 m). 

5. Potentially damaging ground shaking continues for about 60 seconds within 25 miles 
(40 km) of the fault. Humboldt and Del Norte counties are less than 25 miles above the 
CSZ fault plane which dips gently eastward, and wholly within the zone of damaging 
shaking. 

6. Potentially damaging aftershocks occur for several months following the main shock, with a 
few earthquakes in the M6 to M7 range. 

Tsunami Hazard 

The scenario earthquake is assumed to generate a local seismic sea wave or tsunami that will arrive 
just minutes after the earthquake occurs. The lack of warning time from such a nearby event will 
result in higher casualties than if it were a distant tsunami source wherein the Tsunami Warning 
System for the Pacific Ocean could warn threatened coastal areas in time for evacuation. In low 
lying coastal areas, strong shaking should be taken as a warning of a potential tsunami, and 
individuals should immediately move to higher ground. 

The tsunami model for this study was provided by the National Oceanic and Atmospheric 
Administration 1 994 report entitled "Tsunami Inundation Model Study of Eureka and Crescent City, 
California" by Bernard, Mader, Curtis, and Satake. That report produced 1:24,000 scale tsunami 
inundation maps for Eureka and Crescent City, but not for other coastal communities that are 
vulnerable to the tsunami. Those maps are generalized on Maps S-1 and S-2 in Appendix B of the 
present report. The model did not examine the possibility of tsunami bores travelling up river 
valleys. Bores were a hazard in Alaska during the 1 964 tsunami, and emergency planners should 
consider them a possible hazard in the present scenario. 



19 



NORTH COAST SCENARIO 

The NOAA model assumes an incident wave 30 feet (10 m) high in water 150 feet (50 m) deep, 
based on historical tsunamis generated by earthquakes in the M8 to M9 range. The resulting 
approximate run-up is modeled at grid points separated by hundreds of feet, using topographic 
contours separated by tens of feet. This results in a plausible flooding scenario appropriate for 
emergency planning only. It is not intended as a site specific or accurate flooding scenario, because 
it is based on an incident wave of height estimated from the historical record, and an inundation 
model using a widely spaced grid on a rough topographic base. The nature of tsunami effects is 
discussed briefly in this section, as well as in the chapters on Buildings, Highways, Marine Facilities, 
Railroads, Electricity, Water Supply, Waste Water, and Petroleum. 

In Humboldt County the greatest impact on populated areas will be the inundation of the Samoa 
Peninsula, and to a lesser degree the village of King Salmon, which faces the opening of Humboldt 
Bay (Map S-1). Earthquake damage to Highway 255 across the bay to Eureka and northward to 
Areata will compound the tsunami problem by isolating the Samoa Peninsula. A possible refuge 
from the tsunami might be afforded by a 1.5 mile-long by 300-foot-wide ridge of wooded dunes of 
elevation 40 to 70 feet just west of Manila, 2 miles north of Samoa, and 4 miles north of Fairhaven. 
The tsunami impact on the village of King Salmon and the PG&E power plant will be less severe than 
on the Samoa Peninsula, but will compound the damage from intense ground shaking (MMI IX) and 
liquefaction. Humboldt and Areata bays will be choked with debris from the Samoa Peninsula, and 
with spills of hazardous materials from the wood products processing facilities there. 

At Crescent City the tsunami destruction will exceed that which occurred from the 1 964 Alaska 

tsunami. Figure S-3 shows that the 1 964 run-up reached 4th Street, while this scenario postulates 

tsunami run-up reaching 8th Street. Crescent City experienced ten fatalities and over $7 million in 

damage from the tsunami caused by the 1964 Great Alaska earthquake (M9.2). Serious damage 

can be expected to the part of the city and the unincorporated area of Del Norte County that lies to 

the southeast of Front and M streets along the shoreline, as happened in 1 964. This area consists 

of hotels, motels, restaurants, marinas, commercial establishments, and some residences. In 

addition to the force of the wave, damage will result from water driven debris, such as logs, small 

boats, building materials, vehicles, etc. The following accounts from Crescent City of the 1964 

tsunami are instructive: 

"At about 1 :45 a.m. on the morning of March 28, the fourth and most destructive wave 
surged. ...Because the tsunami happened at night, the exact severity of the situation 
was not known until the following day. ...At Citizens Dock and the Crescent City 
Harbor, 26 boats had sunk like bathtub toys. The modern dock facility, built with pride 
only 1 4 years earlier, was a twisted mess. Fishermen on board their boats had to swim 
to safety amid lumber and driftwood as the waves surged and receded. ...The tsunami 
destroyed 29 city blocks in Crescent City, hurling mud, logs and cars into homes and 



20 



NORTH COAST SCENARIO 




Figure S-3 Perspective map showing the extent of flooding (shaded) in Crescent City from the 1 964 Alaska 
earthquake tsunami. Reproduced with permission of W.H. Griffin, Crescent City Printing Co., inc. 
The postulated extent of flooding from the scenario event is dashed for comparison. 



businesses. ...Massive structural damage was left by the tidal wave... and according to the 
mayor Bill Peepe, about 1 ,000 automobiles were destroyed the night of March 27 and the 
early morning of March 28" (Conlin, 1991). 

"Crescent City harbor, especially facilities operated directly by the harbor district, or under 
direct jurisdiction of the harbor district, took a beating that left the area in a state of almost 
total devastation. The lumber wing of Citizens Dock was a shambles, and there were only 
enough piling standing along the main deck approach to the lumber and fish wings to keep the 
sagging floors from falling into the bay. The lumber wing resembled a washboard with planks 
from the dock floor and piling leaning crazily at all angles. The fish wing, newest portion of 
the dock, was in better shape, but had incurred extensive damage. ...Huge logs that, during 
floods on the rivers over the past years, had washed down onto the Del Norte beaches were 
brought in on the crest of the wave (engineers placed its highest crest at 20.78 feet) and used 
as battering rams to contribute to the fury of the force of the water. ...$1,250,000 was 



21 



NORTH COAST SCENARIO 



allocated for cleanup for health and safety reasons, including repair of the ocean outfall of the 
sewer system, replacement of a portion of the seawall, and repair or replacement of the 
devastated harbor facilities. ...Twenty-nine city blocks were left in total or partial ruins, and 
the devastation extended for a distance of approximately 2 miles (3 km) to the south of the 
city limits. Estimates of the cost or replacement of damage and destroyed public and private 
properties were later placed at $16 million" (Griffin, 1984). 

These descriptions resulted from a tsunami originating in Alaska. A tsunami originating locally is 
expected to create more damage to an area that has just suffered intense earthquake shaking. The 
1 964 accounts illustrate the type of damage that can occur, and point out the danger of people 
returning to the evacuation zone after the first wave has receded. In 1 964, the first damaging wave 
hit Crescent City at 1 1 :03 pm, but the fourth wave that hit several hours later was the most 
destructive. 

The 1 992 Petrolia earthquake (M7) generated a small tsunami that arrived after the shaking by 20 
minutes at Eureka and by 47 minutes at Crescent City. Tsunami waves continued to arrive for 10 
hours, and the strongest wave arrived at Crescent City almost 4 hours after the earthquake 
(Gonzales and Bernard, 1992). 

Ground Motion and Intensity 

Shaking intensity maps have been prepared by the California Department of Conservation, Division 
of Mines and Geology and by Evernden of the U.S. Geological Survey for several large strike-slip 
earthquakes. This is our first scenario involving both a non-vertical fault and reverse slip. We 
developed a method to predict the seismic intensity distribution from previous subduction 
earthquakes elsewhere in the world (Petersen and others, 1993). The attenuation of ground 
motions and damage for a great earthquake along the CSZ would probably differ from an earthquake 
on a strike-slip fault due to the differences in fault geometry and radiation of seismic waves. 
Consequently, we have analyzed historical intensity data and peak acceleration attenuation relations 
derived from great earthquakes on subduction zones similar to the CSZ. We used two types of data 
from the global subduction earthquakes to produce an intensity map for the scenario earthquake. 

1 . Global Earthquake Analogy 

We reviewed published maps of observed intensities and aftershock zones for large subduction 
earthquakes that occurred along the margins of the Pacific Ocean, using Pacheco and Sykes (1992) 
for moment magnitude and depth estimates. Crouse (1991) points out that subduction zones with 
characteristics similar to Cascadia exist in southwest Japan, Alaska, Central America, Colombia, 
Peru, and central and southern Chile. Intensity maps and aftershock studies are available for three 
earthquakes in Peru (Beck and Nishenko, 1990), one in Mexico (Reyes and others, 1979; Figueroa, 

22 



NORTH COAST SCENARIO 

1973), and two in the U.S. (Algermissen and others, 1969; Oppenheimer and others, 1993; Stover 
and Coffman, 1993). We determined the configuration of the aftershock zone, estimated the trend 
of the trench, and measured on small scale maps the surface distance from the closest portion of 
the aftershock zone to each of the intensity zones. 

Few of the published intensity data had a well defined MMI IX zone. Therefore, we analyzed the 
MMI IX zone from site-specific intensity data of the 1964 Alaska and 1992 Petrolia subduction 
earthquakes, as well as the 1 906 San Francisco, and 1 872 Owens Valley strike-slip earthquakes 
(Table S-2). During the 1964 Alaska earthquake, the city of Portage, Alaska experienced an 
intensity MMI IX. The best determined focal depths for aftershocks located near the city range from 
6 to 18 miles (10 to 30 km). During the 1906 San Francisco earthquake, the city of Santa Rosa, 
about 17 miles (28 km) from the fault source also experienced MMI IX. Oppenheimer and others 
(1993) indicate that the city of Petrolia, which experienced MMI IX, was 6 miles (10 km) above the 
CSZ fault plane. In addition, several towns located about 1 2 to 15 miles (20 to 25 km) from the 

TABLE S-2 

INTENSITY-DISTANCE RELATIONS FOR SELECTED SHALLOW EARTHQUAKES 

OF DEPTH 10 TO 30 km 



INTENSITY (MMI) 


DISTANCE (kmP 


INTENSITY (MMI) 


DISTANCE (km) + 


Owens Valley, 1872", M8.0 




San Francisco, 1906", M8.0 




IX 


25" 


IX 


28' 


VIII 


55' 


VIII 


70" 


VII 


120' 






Peru, 1942, M8.2 




Alaska, 1964, M9. 2 




VIII 


70 


IX 


20* 


VII 


110 


VIII 


100 


VI 


220 


VII 


210 






VI 


500 


Peru, 1966, M8.1 




Mexico, 1973, M7.3 




VIII 


70 


VIII 


75 


VII 


140 


VII 


150 


VI 


200 


VI 


240 


Peru, 1974, M8.0 




Petrolia, 1992, M7.0 




VIII 


75 


IX 


io- 


VI 


160 


VIII 


ii 






VII 


22 






VI 


32 



x The 1872 and 1906 earthquakes are mainly strike-slip events. The others six are subduction events. 
+ Surface distance from aftershock zone to furthest extent of MMI value listed. 
* Shortest distance to fault rupture plane. 



23 



NORTH COAST SCENARIO 

1872 Owens Valley fault rupture also experienced MMI IX effects. Thus, even though not all sites 
close to the source experienced such high intensities, those sites experiencing MMI IX were 
generally within 1 2 miles (20 km) of the fault rupture plane. 

We also analyzed the intensities from the April 13, 1949 (M7.1) and April 29, 1965 (M6.5) Seattle, 
Washington earthquakes that ruptured near the CSZ, but which are considered to be intraplate 
events (Crouse, 1991). Stover and Coffman (1993) showed that the intensity distributions for the 
1 949 and 1 965 earthquakes were similar, although the 1 949 event was more destructive. The 
intensity pattern for the 1 949 event is asymmetrical and includes a MMI VII zone extending 25 to 
45 miles (40 to 70 km) to the north and east, and 60 to 120 miles (100 to 190 km) to the south 
and west of the epicenter. The MMI VII zones for the Seattle earthquakes are of comparable 
dimensions to the MMI VII zones measured for the global subduction earthquakes we analyzed. The 
distances to each of the intensity zones are shown in Table S-2 and indicate that for each of the 
global earthquakes, the MMI VIII zone generally would extend entirely across the 50 mile (80 km) 
width of our planning area. We assume that the intensities reported from these earthquakes were 
primarily from soil sites, since few population centers are on rock sites. 

2. Instrumental Estimates 

Peak acceleration has been related to earthquake magnitude and distance from the fault. The peak 
horizontal acceleration attenuation relationships of Crouse (1991) and Youngs and others (1988) for 
subduction earthquakes on rock sites are generally compatible. These relations predict lower 
accelerations in the near field and considerably higher accelerations in the far field than the 
attenuation relationships for non-subduction earthquakes derived by Joyner and Boore (1988), and 
Boore and others (1993). The relationship of Youngs and others (1988) was particularly suited to 
our scenario earthquake because it uses the distance between the site and the fault plane. This 
relationship does not predict the high accelerations recorded during the 1 992 Petrolia earthquake. 
Three of these exceeded 0.5 g or half the acceleration of gravity (Shakal and others, 1992), while 
the Youngs and others (1988) relationship for M7 would have predicted maximum accelerations for 
rock sites of only 0.17 g. This large discrepancy results partly from the effects of site geology and 
of topography. Consequently, we corrected for the geologic site effects. 

We used the conversion relationship established by Trifunac and Brady (1975) from western United 
States earthquakes between MMI and peak horizontal acceleration. The conversion predicts 
intensity values that are well within the envelope formed by other conversion equations (Applied 
Technology Council, 1985). To test the applicability of the Trifunac and Brady (1975) relationship 
to the Cascadia subduction region, we converted the observed peak horizontal accelerations of the 



24 



NORTH COAST SCENARIO 

1992 Petrolia earthquake (Shakal and others, 1992) to MMI and found reasonable correspondence 
with the MMI contours shown by Oppenheimer and others (1993). 

For M8.4 and a distance of 12 miles (20 km), Youngs and others (1988) predict a shaking 
acceleration of 0.24 g (on rock-like material), which converts to MMI VIII according to Trifunac and 
Brady (1975). The MMI IX zone was commonly observed in past earthquakes at a distance of 12 
miles (20 km) from the rupture as indicated in Table S-2. We used a site correction of one intensity 
unit to bring the MMI VIII on rock-like material (shear wave velocities (v,) > 2,500 feet/sec or 750 
m/s), up to MMI IX on alluvium. This assumes that rock-like material having v, greater than 750 
m/sec has a site correction that is halfway between hard rock (v, > 5,000 feet/sec, Fumal and 
Tinsley, 1 985) having zero correction, and alluvium (v, < 1 ,200 feet/sec) having a correction of 
+ 2 MMI units (Table S-3). Thus the amplitudes of our intensity values are guided by the historical 
MMI data while their attenuation with distance follows the relationship of Youngs and others 
(1988). 

To test the intensities that we derived for the scenario earthquake, we compared the intensities that 
would be expected from the Evernden and Thomson (1985) model and found reasonable agreement. 
Evernden (1993) ran his model for a line source at a depth of 15 km on the CSZ in the vicinity of 
Eureka, resulting in MMI IX on alluvium in coastal Humboldt and Del Norte counties, similar to our 
results. Our results are consistent with Heaton and Hartzell (1987), who used strong motion 
simulation methods to predict high accelerations of 0.6 g near the coast from subduction events, 
which corresponds to about MMI IX using Trifunac and Brady (1975). 

Geologic Corrections 

To account for the effects of geology, the intensity map was overlain by a geologic map for which 
each geologic unit was assigned a shaking intensity correction factor. The magnitude of this factor 
reflects the anticipated amplification of seismic shaking which occurs on geologic materials that are 
softer than crystalline bedrock. Table S-3 lists the geologic age and type of rocks in the map area 
and the shaking intensity correction factor assigned to each. Evernden and others (1981) have a 
range of 3 units for the correction factor, whereas we have a range of only 2 units because we 
consider liquefaction effects separately. Our classifications for some geological units also differ 
slightly from Evernden and others (1981). For instance, shear wave velocities have been found to 
be greater in Pleistocene deposits than in Holocene deposits (Fumal and Tinsley, 1985). Thus, we 
consider Pleistocene sedimentary deposits to be slightly more consolidated and to have slightly less 
intensity amplification ( + 1.8) than Holocene sedimentary deposits ( + 2.0). The anticipated MMI 
distribution for the scenario earthquake is determined by adding the correction factor to the intensity 
calculated for crystalline bedrock, and rounding to integer values. Half integers are shown only for 



25 



NORTH COAST SCENARIO 

TABLE S-3 
GEOLOGIC UNITS AND SHAKING INTENSITY CORRECTION FACTORS 



GEOLOGIC UNITS 


RELATIVE INTENSITY 
ADDITION FACTOR 


Plutonic and Metamorphic Bedrock 

Volcanic Rocks 

Jurassic and Cretaceous Sedimentary Rocks 

Late-Cretaceous to Eocene Rocks 

Miocene Sedimentary Rocks 

Mio-Pliocene to upper-Pliocene Sedimentary Rocks 

Early to middle-Pleistocene Sedimentary Rocks 

Holocene & Holo-Pleistocene Sedimentary Deposits 


0.0 
0.3 
0.8 
1.2 
1.5 
1.7 
1.8 
2.0 



the MMI VIII range: 8- indicates 8.0 to 8.4, and 8+ indicates 8.5 to 8.9. The half integers help to 
differentiate between Late Cretaceous to Eocene rocks having a geological factor of 1.2 and rocks 
having geological factors of 1.7 (Mio-Pliocene) to 1.8 (Pleistocene), which will shake more strongly. 

Intensities greater than MMI IX are not shown on Maps S-1, S-2, and S-3 because MMI X through 
XII are generally attributed to the secondary effects of ground breakage (faulting, liquefaction, 
landslides) which are identified separately. 

Shaking Effects Predicted 

Maps S-1, S-2, and S-3 show that shaking intensities are generally greatest near the coast and 
decrease inland. This pattern is modified by the areal distribution of geologic materials that vary in 
their response to shaking. For alluvial sites the MMI IX zone extends about 45 miles (70 km) inland 
from the coast in southern Humboldt County, and about 6 miles (10 km) inland from the coast in 
northern Del Norte County. For bedrock (v, > 5,000 feet/sec or 1,500 m/s), the intensities are 
rarely above MMI VII. Overall, the predicted intensities are high because the fault plane is directly 
beneath most of Humboldt and Del Norte counties at depths of 6 to 12 miles (10 to 20 km). 



The large MMI VIII + areas generally are adjacent to and often surround the MMI IX areas and cover 
the hills above Humboldt Bay and the Eel River Plain. This zone also includes small parts of the 
southeast portion of the Smith River Plain, the Garberville-Redway area, and the alluvial river valleys 

26 



NORTH COAST SCENARIO 

on the east side of the study area. Most of the three main population centers of the study area, 
Eureka, Areata, and Crescent City, are in MMI VIII + to IX areas. The MMI VIII- area includes 
mountainous terrain of the southwest portion of the study area and includes the small towns of 
Shelter Cove, Honeydew, and Petrolia. 

The MMI VII area is the largest intensity zone. It covers the mountainous terrain of the southeast 
and central portions, and the northern portion except the Smith River Plain. There are no large 
population centers in the MMI VII zone. 

Local intensities could be greater than those from shaking only, mainly due to liquefaction in alluvial 
areas, and landslides in hilly areas. 

Long period motion can shake tall structures at large distances from M^7 earthquakes. For 
example, the M7 earthquake that occurred on the Mendocino fault in 1 994 caused some concern to 
people in high rise buildings about 220 miles (350 km) away in Sacramento. The scenario 
earthquake would generate such long period motion as far away as Sacramento and San Francisco. 

Ground Failure 

Ground failure or ground breakage occurs when there is a permanent deformation of soil or rock. 
Ground failure, which can result in MMI > IX (Appendix A), can occur in isoseismal zones for which 
we would predict MMI values as low as VI based on shaking alone. Because ground failure results 
from special local conditions, we do not show MMI > IX on our regional maps. We present ground 
failure potential separately because it presents different engineering problems than does ground 
shaking alone. 

Areas of potential ground failure on Maps S-1, S-2, and S-3 that could have intensities greater than 
MMI IX include: 

a) Areas where the high water table and other ground conditions favor liquefaction. 

b) Areas of potential landsliding, comprising much of the mountains in the planning area. 

c) The areas of surface rupture on the Little Salmon fault. 

Fault Rupture 

The Alauist-Priolo Earthquake Fault Zoning Act 

The Alquist-Priolo Earthquake Fault Zoning Act was enacted in 1 972 to mitigate the hazard of 
surface fault rupture along active faults in California. The purpose of this Act is to avoid building 
structures for human occupancy across traces of active faults. Responsibilities for carrying out the 

27 



NORTH COAST SCENARIO 

provisions of the act are shared by State and local government. Specifically, the State Geologist 
(Department of Conservation, Division of Mines and Geology) is required to establish regulatory 
Earthquake Fault Zones (EFZs) for those faults considered to be "sufficiently active and well defined 
as to constitute a potential hazard to structures from surface faulting or fault creep." Cities and 
counties must regulate most building projects for human occupancy within the EFZs by requiring 
geologic investigations before issuing development permits. Some faults (Little Salmon, Hydesville, 
etc.) in the scenario area have been zoned under the Act. 

The effectiveness of the Fault Zoning Act varies from place to place, depending largely on how well 
a particular fault is defined. Even so, the law only applies to new real estate development and to 
structures for human occupancy. Many structures, such as Highway 101 Overhead near Fields 
Landing and the southern part of the College of the Redwoods, sit astride or adjacent to the active 
trace of the Little Salmon fault. The extent of damage will depend on the amount of displacement 
that occurs locally on the fault and on measures taken to mitigate the hazard. 

Rupture Postulated for the Little Salmon Fault 

Displacement on the Little Salmon fault has likely accompanied previous large CSZ earthquakes 
(Clarke and Carver, 1992). Consequently, we assume that in addition to the main faulting on the 
CSZ, subsidiary faulting averaging 6 feet (2 m) and up to 12 feet (4 m) will occur on the Little 
Salmon fault across a zone tens of feet wide. This fault dips about 1 5° to the northeast. The EFZ 
extends from Highway 101 near the Fields Landing Overhead to College of the Redwoods and along 
the base of the hills northeast of Fortuna. This fault has been active during Holocene time and has a 
high potential for surface rupture in future major earthquakes on the CSZ (Carver, 1 993; Wills, 
1990; Carver and Burke, 1987b). The EFZs for the Little Salmon fault are appended to this scenario 
report. 

Liquefaction 

Areas with potential for ground failure due to liquefaction in this scenario earthquake were identified 
and plotted on Maps S-1, S-2, and S-3. Three factors must be present for liquefaction to occur: 

1 . A high water table. 

2. Layers of loose sand. 

3. Earthquake shaking of intensity greater than MMI VI. 

Liquefaction susceptibility has been divided into two categories, high, and moderate to low. High 
susceptibility has been assigned to areas that have experienced liquefaction during past earthquakes 
and to alluvial areas having deposits of liquef table sediments with groundwater within 1 feet (3 m) 
of the surface. These areas generally include artificial fills and natural deposits of bay mud, beach 

28 



NORTH COAST SCENARIO 

and dune sands, lake deposits, and active stream channels of Holocene age. Moderate to low 
susceptibility has been assigned to alluvial areas thought to contain limited liquet iable sediments 
where the groundwater table is at a depth of 10 to 30 feet (3 to 10 m). These areas include 
elevated river and marine terraces, older dune sand, and alluvial fans. Only scattered incidents of 
liquefaction are expected to occur in the moderate to low susceptibility areas. 

The presence of a "free face" immediately downslope from a site increases the potential for 
liquefaction. In general, free faces exist along the banks of canals, rivers, channels, ponds, streams, 
lakes, and bays. 

Seismic shaking will be sufficient to cause liquefaction in susceptible sediments throughout the 
study area. Much of the development in the southern half of the planning area is underlain by 
Holocene alluvial sediments which are susceptible to liquefaction. The areas delineated on Maps 
S-1, S-2, and S-3 as having high potential for ground failure include all deposits below high tide and 
fine fluvial deposits near the major rivers and creeks. 

Crescent Citv 

The northern half of the planning area is less susceptible to liquefaction because most of the area is 
underlain by consolidated sedimentary, igneous, volcanic, or metamorphic rock. The main 
population center is on the Crescent City platform. Although it is relatively flat land with a relatively 
high water table, the platform and its overlying beach deposits are of Pleistocene age (Davenport, 
1982). Due to consolidation and cementation over time, deposits of this age in California have not 
been known to liquefy in modern times (Youd, 1994; Dwyer and Borchardt, 1994). There are only a 
few known cases of liquefaction in materials older than Holocene age. In the U.S., these have been 
associated with the Borah Peak, Idaho (1983), New Madrid (191 1-1912), and Charleston (1886) 
earthquakes. Liquefiable deposits in the Crescent City area are confined mostly to the Holocene 
dune sands northwest of Lake Earl. 

In preparing the intensity maps, we tentatively considered units Q (young alluvium) and Qs (dune 
sand) of Wagner and Saucedo (1987) to have high liquefaction potential and units Qby (late 
Pleistocene Battery Formation) and Qt (late Pleistocene river terrace) to have low liquefaction 
potential. Next, we modified this by using the water table data of Back (1957). 

Judging mostly by the coarseness of the deposits, TerraScan (1976) considered liquefaction to be 
unlikely in the Smith River, Hiouchi, Gasquet, and Klamath-Klamath Glen areas. For Smith River, 
they wrote: 



29 



NORTH COAST SCENARIO 



"The possibility of liquefaction beneath the town of Smith River, or immediate environs, is 
considered minimal. Information from water wells in the area suggests that the area is 
underlain by fan deposits and terrace material that are not conducive to liquefaction. ...It is 
possible that liquefiable materials are present beneath the flood plain of the Smith River, but 
this remains conjectural" (p. 18-19). 



For Klamath, they wrote: 

"Alluvial materials underlying the flood plain of the Klamath River and small tributary valleys 
are not likely to result in significant liquefaction because of their coarse consistency" 
(TerraScan, 1976, p. 21). 



Humboldt Bay 

In the Humboldt Bay area, the record of ground failure during earthquakes is substantial. 
Kilbourne and others (1980) show 42 localities, most of which experienced liquefaction in 
earthquakes that occurred in 1853, 1865, 1906, 1932, 1954, 1975, and 1980. The 1991 
Honeydew earthquake (M6.2), triggered liquefaction along the Mattole River and Honeydew Creek 
channels (McPherson and Dengler, 1992). The M7 mainshock of the 1992 Petrolia earthquakes 
triggered extensive liquefaction in floodplain deposits of the Eel, Mattole, and Salt rivers (Prentice 
and others, 1992). 

Our delineation of the zone of potential liquefaction was hampered by the lack of a water table 
contour map that we could use to distinguish between the zones of high and medium to low 
liquefaction potential within the alluvial units. The water well logs (Evenson, 1959) and 
geotechnical boring logs (Stevens, 1 993) in the area generally show water levels in the young 
alluvial areas to be within 1 feet (3 m) of the surface at least part of the year. 

Landslides 

Nearly every large earthquake in a hilly area will produce seismically induced landslides (SIL), 
depending somewhat on the previous seasonal rainfall. The 1991 and 1992 earthquakes 
triggered hundreds of landslides, mostly associated with the road system, with one slide 
temporarily blocking Singley Creek (Dunklin, 1992). Lifelines are affected by two SIL effects: 
noncohesive falls and cohesive slides. Noncohesive falls include rock falls, soil falls, disrupted soil 
slides, and rock slides. Falls generally impact lifelines from above by depositing rocks that can 
cause disruption. Cohesive slides include rock slumps, soil slumps, rock block slides and slow 
earth flows. Slides generally affect lifelines from below by displacing supporting material. 



30 



NORTH COAST SCENARIO 

During a great earthquake, such as the scenario event, the formation of large landslide dams 

across major streams poses yet another hazard. Monitoring this hazard via overland travel will be 

virtually impossible. As Dunklin (1992) wrote: 

"... [reconnaissance will be] difficult since many of the logging roads needed to reach 
remote areas are impassable due to fill failures, slumps, or rockslides" 
(p. 198). 

Areas especially subject to SIL are shown on Maps S-1, S-2, and S-3. Not all the areas shown as 
susceptible to landslides will fail in this way, and some landslides could occur in areas not 
mapped as susceptible. Also, as a result of the scenario earthquake scattered landslides or rock 
falls will occur in susceptible areas outside of the scenario planning area, particularly during the 
rainy season. Techniques for analyzing SIL potential have been developed and used to produce a 
large scale map for San Mateo County (Wieczorek and others, 1986). These techniques can be 
applied on a site by site basis when the character of the bedrock is known (Wilson and Keefer, 
1985), but for our regional analysis we used a more general approach. Three steps were taken to 
prepare the SIL overlay: 

1 . Known Landslides 

Large landslides were compiled from various references. Many of these previously mapped 
landslides are likely to be reactivated by the scenario earthquake (Carver, 1993). 

2. Potential Coherent Slides 

Slopes of greater than 30 percent and less than 70 percent are shown as having a high 
potential for coherent slides in certain types of rock whenever the MMI is greater than VII. 
For most rock types the potential for coherent slides is moderate in MMI zones of VII or 
less. The potential for SIL usually increases with slope, but even the most unstable materi- 
als seldom experience SIL unless the slope is over 30 percent (Keefer, 1984). If the 
earthquake occurs in conjunction with unusually high moisture levels associated with the 
end of the rainy season or with improper drainage, even normally stable materials may fail. 
In the 1 989 Loma Prieta earthquake (M7), most cohesive slides occurred in the area of 
MMI VIM or stronger shaking (Spittler and others, 1990; Manson and others, 1991). 
Because this scenario is for an M8.4 event of much longer duration (60 seconds vs. 15 
seconds) than the 1 989 event, we assume there will be some coherent slides in the MMI 
VII zone as well. 

3. Potential Noncoherent Slides 

Slopes steeper than 70 percent are shown as having a potential for noncoherent falls. 
Loose materials at the angle of repose (typically 33 to 37 degrees, or 65 percent to 75 

31 



NORTH COAST SCENARIO 

percent slope) require only a slight horizontal acceleration to cause them to tumble down 
slope. Falls are common in MMI zones as low as VI (Keefer, 1984). We expect most of 
the steep areas to have noncoherent falls. There also will be numerous falls from steep 
road cuts in both counties. Further, beneath each steep slope lies a "runout" zone of about 
half the height of the slope wherein noncoherent falls may impact (Keefer, 1991). Some of 
these slopes could be affected by coherent slides as well. Most of these steep zones are 
not near populated areas, and should have only localized effects on lifelines. 



32 



BUILDINGS AND STRUCTURES 



SCENARIO MAPS AND DAMAGE ASSESSMENTS 

ARE INTENDED FOR EMERGENCY PLANNING 

PURPOSES ONLY 



THEY ARE BASED ON THE FOLLOWING HYPOTHETICAL 
CHAIN OF EVENTS: 

1 . A PARTICULAR EARTHQUAKE OCCURS 

2. VARIOUS LOCALITIES IN THE PLANNING AREA 
EXPERIENCE A SPECIFIC TYPE OF SHAKING OR 
GROUND FAILURE 

3. CERTAIN CRITICAL FACILITIES UNDERGO DAMAGE AND 
OTHERS DO NOT 

THE CONCLUSIONS REGARDING THE PERFORMANCE OF 
FACILITIES ARE HYPOTHETICAL AND AND NOT TO BE 
CONSTRUED AS SITE-SPECIFIC ENGINEERING EVALUATIONS. 
FOR THE MOST PART, DAMAGE ASSESSMENTS ARE STRONGLY 
INFLUENCED BY THE SEISMIC INTENSITY DISTRIBUTION MAP 
DEVELOPED FOR THIS PARTICULAR SCENARIO EARTHQUAKE. 
THERE IS DISAGREEMENT AMONG INVESTIGATORS AS TO 
THE MOST REALISTIC MODEL FOR PREDICTING SEISMIC 
INTENSITY DISTRIBUTION. NONE HAVE BEEN FULLY TESTED 
AND EACH WOULD YIELD A DIFFERENT EARTHQUAKE 
PLANNING SCENARIO. FACILITIES THAT ARE PARTICULARLY 
SENSITIVE TO EMERGENCY RESPONSE WILL REQUIRE A 
DETAILED GEOTECHNICAL STUDY. 

THE DAMAGE ASSESSMENTS ARE BASED ON THIS SPECIFIC 
SCENARIO. AN EARTHQUAKE OF SIGNIFICANTLY DIFFERENT 
MAGNITUDE ON THIS OR ANY ONE OF MANY OTHER FAULTS 
IN THE PLANNING AREA WILL RESULT IN A MARKEDLY 
DIFFERENT PATTERN OF DAMAGE. 



NORTH COAST SCENARIO 

BUILDINGS AND STRUCTURES 
Introduction 

Seismic performance provisions in California building codes are intended to protect life and reduce 
the potential of property damage. Even though it is not yet possible to precisely forecast the exact 
magnitude, time, and location of the next earthquake, it is apparent that the existing building stock 
in California will be subjected to damaging earthquakes. By establishing the year 1 933 (Long Beach 
earthquake) as an applicable baseline in the development of earthquake-resistant design, it has 
become possible to develop a general relative scale for an overall understanding of the seismic 
performance and vulnerability (i.e., hazard potential) of representative building classes to 
earthquakes. For a definitive source of building classification methods, refer to Algermissen and 
Steinbrugge (1978). In the development of seismic building codes and improved earthquake- 
resistant design since 1 933, experience provides us with relationships between building classes, 
construction types, and their seismic performance that allows for the damage assessment of classes 
of structures on a collective, technical, and probabilistic basis. 

Earthquake scenarios describing damage patterns and damage estimates are not precise predictions 
of what will occur, but are objective assessments developed for emergency planning. A statement 
that a building, facility, or lifeline system will survive, remain operable, or be severely damaged, can 
be given only in probabilistic terms. 

According to Steinbrugge and others (1978, p. 79): 

"One cannot predict that a person who is driving under the influence of alcohol will 
certainly have an accident, but one can state that the probabilities are significantly 
higher than if he were not. Knowing building construction types and past earthquake 
performance of structures with given characteristics, realistic scenarios of probable 
damage can be developed for use in disaster response planning. ...The numerical 
values associated with each response planning topic represent reasonable maximum 
expected conditions. In other words, these values are credible; they have past data 
or experienced judgement behind them. The quality of the numbers vary depending 
upon the extrapolation of past data, the reliability of the assumptions supporting the 
calculations, and the quality of judgement behind the decisions." 

The actual effects that earthquakes have on buildings and facilities depends on many variables, 
including: 

1 . Magnitude of the earthquake 

2. Geological characteristics of the site 

3. Location of earthquake 

4. Severity and duration of ground shaking 

5. Ground response according to soil types 

6. Soil structure interaction 



33 



NORTH COAST SCENARIO 



7. Code provisions in force at the time of the building's design 

8. Building construction type, configuration, and size 

9. Quality of construction 

10. Proper building maintenance by the owner once the building is occupied. 

One of the most important variables used to assess a building's seismic performance is its date of 
construction. Building code provisions are normally not retroactive and many existing buildings have 
not had the benefit of advanced performance standards that were developed after construction. For 
one recent exception to this, refer to the section on unreinforced masonry buildings. 

Seismic Considerations 

Building Damage and Ground Motions 

The success with which a building responds to the dynamic loads induced by earthquake ground 
motions determines the level of its seismic performance. Seismic performance standards for 
buildings provide for life safety (i.e., to protect life) and are only partially directed toward damage 
control. Exceptions include the 1973 California Hospital Act and the 1933 Field Act. 

The "life safety" approach is based on an underlining philosophy that earthquake-resistant design be 
used to develop the capacity of structures to "resist major earthquakes of the intensity or severity of 
the strongest experienced in California without collapse, but with some structural as well as 
nonstructural damage. In addition, the code indicates that "In most structures, it is expected that 
structural damage, even in major earthquakes, could be limited to repairable damage." Design for 
damage control usually encompasses life safety, however, design for life safety (i.e., minimum code 
standards), does not necessarily include damage control. 

The following description of earthquake ground motions and building response is abstracted from 

Steinbrugge and others (1987, pp. 80-82). 

"Human observations as well as seismographic records show that the very rapid and 
violent ground oscillations (short period motions) in the epicentral regions are quickly 
damped and dispersed, leaving principally slower long-period motion at the greater 
distances from the earthquake source. The greater the distance, the slower the 
observed predominant oscillations. The predominant oscillations at large distances from 
the earthquake can be so gentle that they may not be felt by all persons, and yet be 
strong enough to cause water in reservoirs to oscillate with some destructive effects. 

Buildings respond differently to different kinds of ground motion. Each building has its 
own specific vibrational characteristics based on its stiffness. Each building will 
therefore respond to the particular ground motion at the site in a specific manner. One 
of these vibrational characteristics is termed the structure's natural period of vibration. 
In general, the taller the building, the longer is its natural period of vibration. If the 
building's natural period of vibration roughly coincides with a few cycles of the principal 
motions of the earthquake, quasi-resonance will occur. As a result, the vibratory motions of 

34 



NORTH COAST SCENARIO 



the building may dramatically increase, along with damage. Damage from quasi-resonance is 
generally observed in taller buildings from distant earthquakes. 

Based on the changes in ground motions as a function of increasing distance, observed 
damage patterns tend to reverse with distance. Damage to low, rigid (short-period) 
buildings predominate over high-rise (long-period) damage in the epicentral and energy- 
source regions nearer the fault. At distances over 100 miles, for example, high-rise 
building damage may predominate over that of even poorly built one-story structures. 
This was dramatically evidenced in Mexico City during the September 1 985 earthquake. 

The historical damage patterns are associated with short-period motions (i.e., rapid 
back-and-forth motions). Isoseismal maps are based on short-period effects. In general, 
light mass structures perform much better than do heavier mass structures. 
Conceptually, this is due to the fact that the ground moves away from the structure 
during an earthquake, and the structure must follow these movements. The heavier the 
mass of the structure, the greater will be the inertial (resisting motion) force on the 
structure. Therefore, a "heavy substantial" building which is not designed to be 
earthquake resistant is more likely to fail than a "flimsy" wood frame structure. 
Countless examples of this exist throughout the historic record. 

Long-period motion principally affects high-rise buildings. An excellent example of long- 
period effects is demonstrated by the 1 952 Kern County, California, earthquake. This 
earthquake resulted in numerous instances of nonstructural damage to multi-story steel 
or concrete frame buildings in Los Angeles and Long Beach, but essentially no damage 
to one- and two- story buildings of any kind in the same area. These cities are located 
70 to 90 miles from the epicenter. Generally, the affected buildings were 10 to 12 
stories high and had a measured natural period of vibration of 1 to 2 seconds, but 
buildings as low as 6 stories were also damaged. (The many modern high-rise 
structures of over 20 stories did not exist then.)" 



Building codes have been one of the principal mechanisms used to reduce the damaging effects of 
earthquakes. The record indicates that earthquake-resistant designs are effective. Most major 
structures perform well. Exceptions have occurred when: 

a) The design barely meets the minimum standards. 

b) The building is not built according to the architect's or engineer's specifications. 

c) The building owner modifies structural components of the building after its occupancy. 

Special Earthquake Hazard Mitigation Legislation In California 

The Field Act 

After the 1 933 Long Beach earthquake, the California Field Act for the safety of public schools was 
enacted and assigned to the Office of the State Architect. As evidenced by the 1 952 Kern County, 
1 983 Coalinga, 1 987 Whittier-Narrows, and 1 989 Loma Prieta earthquakes, the resulting higher 
standards proved to be very successful. During the immediate emergency recovery period after the 
1 989 Loma Prieta earthquake, for example, the Marina Middle School successfully served as a 
shelter for the homeless and as an emergency services command post in the severely damaged 
Marina District of San Francisco. 

35 



NORTH COAST SCENARIO 

The Field Act originally applied only to new public schools (private schools were not included in the 
mandate). As the act was not retroactive, all remaining older public schools throughout California 
continued to be used. However, in 1 969, the Garrison Act was enacted as follow-up legislation to 
deal with the difficult task of abating the hazard posed by the older public schools still in existence, 
and required the abatement of hazardous older schools by 1 978. Few non-Field Act public schools 
remain, although some older private schools still pose an earthquake hazard. 

Hospital Act and Unreinforced Masonry Building Abatement Act 

In addition to the Field Act, three other special California earthquake laws were enacted in 1 973, 

1986, and 1993: 

1. The 1973 Hospital Act which was adopted after the 1971 San Fernando earthquake. 

2. The Unreinforced Masonry (URM) Building Act (also known as Senate Bill 547 and later as 
Section 88-75) enacted in 1986. 

3. An earthquake hazard disclosure requirement for residential dwellings adopted as part of 
the provisions in the Business and Professional Code (originally proposed as Assembly Bill 
200) implemented in January 1993. 

All three provisions are state mandated and developed to improve the seismic performance of 
buildings. 

Potentially Hazardous Buildings 

Certain types of buildings have had a much greater incidence of earthquake damage than others. 
These are often designated as potentially hazardous buildings. The most common types of 
potentially hazardous buildings found in the Humboldt and Del Norte County areas include: 

1 . Unreinforced masonry buildings 

2. Pre- 1940 wood frame houses 

3. Tilt-up buildings 

4. Pre-mid 1 970s concrete frame buildings 

5. Mobile home 

Each of these is discussed below. Planners must be aware of the hazards that they present, 
including the consequences and impact of their failure on the local community. 

Unreinforced Masonry Buildings 

These are old brick buildings (Figure B-1) built in the 1930s or before. Some are historic structures. 

URM structures, particularly bearing-wall structures, are classified as one of the more hazardous 



36 



NORTH COAST SCENARIO 




Figure B-1 Typical unreinforced masonry bearing wall building (URM). From Lagorio and others (1986). 



forms of construction found in the United States. After a strong earthquake, those that have not 
collapsed are usually so heavily damaged that in many cases demolition is required. 

URM buildings have several typical characteristics. First, they do not have steel reinforcing in the 
wythes of brick, hence the name "unreinforced masonry." Second, they are often built with weak 
mortar, or mortar that has deteriorated with age. Many also lack metal ties connecting the walls 
with floor or roof structural members. It is this latter characteristic, in particular, that makes these 
structures a hazard. During an earthquake, exterior walls often fall outward, creating a serious life 
safety risk to pedestrians or people running from the building (Photo B-1). 

Cities in Uniform Building Codes Seismic Zone 4 in California are required by the state, under Senate 
Bill 547, to identify and mitigate the hazards of existing URM buildings in their jurisdiction. 

URM Buildings in the Study Area 

As in other older jurisdictions of California, principal cities in the study area also have an inventory 

of existing URM buildings. Typically, these URM buildings, which range from one to four stories, are 



37 



NORTH COAST SCENARIO 




^ 

n ^ 






a? 




&~-- 



j±*± 




Photo B-1 Unreinforced brick buildings frequently lose parts of walls in earthquakes. Falling brick is a major 
life-safety concern. This structure was damaged in the 1987 Whittier earthquake. 
Photo by Ronald Gallagher. 

concentrated in the older downtown areas of cities. Occupancy of this building class tends to be 
related to industrial, commercial/mercantile (retail stores, offices, etc.), apartments, and hotel uses. 

There are relatively few URM buildings in the study area because wood remains the principal 
building material. All principal cities (Eureka, Areata, Fortuna, Crescent City) were visited and local 
building officials were consulted about the status of URMs in their communities. Eureka has 
approximately 25 URM buildings in the older waterfront/central business district area (refer to 
Figure B-2). The other communities have few or no URMs, and where they exist URMs are 
separated widely in the older areas of these towns. For example, Areata has about three URMs 
located in the general vicinity of the city square. 

EERI (1990, p. 127) gives the following description of URM damage: 

"Much of the spectacular building damage that resulted from the Loma Prieta earthquake was 
suffered to pre-code structures, principally the unreinforced masonry type (URM). Such 



38 



NORTH COAST SCENARIO 



buildings, constructed of wood-frame roof and floor systems supported by thick unreinforced 
brick walls, were commonly constructed throughout California before the adoptions of building 
codes with provisions to make buildings seismic-resistant. ...Unreinforced masonry buildings 




aen£ML 

HOSPITAL 

ICMMSTENKN 
Ian I i 



Figure B-2 Schematic distribution of URMs in Eureka. 

failed in areas close to the earthquake epicenter and as far away as San Francisco and Monterey. 
...The major shaking in and around Santa Cruz contributed to heavy damage to the unreinforced 
masonry buildings, particularly in the Pacific Garden Mall. Because unreinforced masonry 
buildings are non-ductile, brittle structures whose lateral systems are incapable of dissipating 
energy in an inelastic manner, the strength of these short-period buildings must exceed the 
product of their reactive weight and the peak ground acceleration in order to survive seismic 
shaking. Many of the buildings failed. The observed modes of failure were similar to those that 
occurred in other earthquakes: out-of-plane brickwork failure, diaphragm flexibility/failure, in-plane 
brickwork failure, and pounding." 

Totals according to types of damage patterns suffered by URM buildings in the San Francisco 
experience are summarized below in Table B-1 . 



39 



NORTH COAST SCENARIO 



TABLE B-1 



TYPES OF DAMAGE TO URM BUILDINGS IN THE CITY OF 
SAN FRANCISCO AFTER THE 1989 LOMA PRIETA EARTHQUAKE 

Source: EERI, 1990, Table 5. 1 



TYPES OF DAMAGE 


NUMBER OF 




BUILDINGS 


Falling individual units or Trim 


103 


Veneer damage or delamination 


100 


Falling of portion of the wall 


61 


Falling of entire wall 


36 


"X" cracks in spandrels 


125 


Vertical cracks in spandrels 


176 


Pies or walls ("X" or stepped cracking) 


198 


Horizontal cracks at top/bottom of pier 


201 


Damage from debris from adjacent buildings 


7 


Roof or floor failure due to movement of exterior wall 


13 



For the 1954 Eureka earthquake (M6.5) Steinbrugge and Moran (1957) state: 

"Building damage was generally minimum or slight, with exceptions which are discussed 
later. There was practically no damage to reinforced concrete, reinforced hollow 
concrete block and wood frame buildings. Unreinforced brick masonry with sand lime 
mortar took the brunt of the damage. On the other hand, the authors saw no damage to 
brick masonry wherein cement mortar and reinforcing steel were used." 



The Eureka experience is summarized in Table B-2. 



During the 1 994 Northridge earthquake, a further record was obtained on the performance of URM 

buildings by comparing retrofitted URM building with those still in their unretrofitted state: 

"Observations are that retrofitted URM buildings performed better than unretrofitted 
ones. Even so, some retrofitted buildings suffered parapet and wall damage, and a few 
wall collapses occurred. Unretrofitted URM buildings generally suffered more extensive 
damage, and a significant number of partial or complete collapses were observed. 
Typical damage to 2-story commercial/ residential unretrofitted URM construction 
included the falling of parapets, shear cracking of walls, the failing of walls loaded 
normal to their plane, and partial collapse because of the loss of corner piers" (EERI, 
1994). 



In this scenario, most cities with URM buildings will have strong ground shaking intensities of MMI 
IX. Damage to those URM buildings will be severe and extensive. For planning purposes, we 
assume that URM buildings in Eureka, Areata, and Crescent City will partially collapse. 



40 



NORTH COAST SCENARIO 



TABLE B-2 



DAMAGE TO PRIVATE BUILDINGS WITH MASONRY WALLS IN EUREKA 
AFTER THE 1954 EARTHQUAKES 

Source: Steinbrugge and Moran (7957) 



WALL MATERIAL 


NUMBER OF BUILDINGS DAMAGED 




MINIMUM DAMAGE* 


SLIGHT DAMAGE 8 


MODERATE DAMAGE 6 


Brick 

Reinforced concrete 

Hollow concrete block E 


4 
8 

7 


14 
5 

1 


4 





incidental plaster damage, glass breakage, possibly small chimney damage. Some with no 

apparent damage. 
B Same as "Minimum" except more extensive, especially with respect to plaster damage; no 

significant structural damage. 
c Loosened and cracked masonry parapets; buildings readily repairable; loss usually less than 10 

percent of building value. 
°With sand-lime mortar and no reinforcing steel; not to be confused with reinforced grouted 

brick masonry construction which may be earthquake-resistant. 
E Probably many are reinforced and have other than sand-lime mortar. 



Pre-1940 Wood Frame Houses 

Because of the history of the timber industry in the study area, wood frame buildings (Figure B-3) 
are the most common type of construction in Humboldt and Del Norte counties. Most wood frame 
structures are single-family dwellings with stud walls. Well-designed wood frame structures have a 
very good earthquake performance record, but an important class of wood frame dwellings has had 
major problems. 

Wood frame dwellings built before 1 940 often shift on or fall off their foundations during 
earthquakes. This has been due to lack of foundation anchorage, unbraced post and pier 
support, or weak cripple walls (cripple walls are those walls between the foundation and the first 
floor). The dwellings become unusable and may be posted "unsafe" by the local building 
department after a major earthquake. While the life-safety risk is low, repairs can be expensive, and 
the occupants must find new shelter during the reconstruction. 

During the 1992 Petrolia earthquake (M7), damage to pre-1940 house was wide spread in the 

strongly shaken areas. 

"...most of the buildings that suffered damage in this earthquake were wood frame houses 
and one and two-story wood frame commercial buildings. Homes slid off foundations. 
Chimneys collapsed" (EERI, June 1992a). 



41 



NORTH COAST SCENARIO 




Figure B-3 Typical pre-1 940 wood frame building. Lagorio and others, 1986. 

NOTE: Foundations are commonly post and pier in Humboldt and Del Norte counties. 

Elevated unbraced foundations collapsed on more than a dozen Ferndale houses (Photo B-2). While 
much of this damage was repairable, some houses were a total loss. This damage imposed an 
added burden on the community of finding shelter for the inhabitants at a time when community 
resources were already severely taxed. 

The State of California recently enacted, under Assembly Bill 200, a requirement for earthquake 
hazard disclosure for residential dwellings. After January 1, 1993 (as required under provisions of 
the Business and Professional Code), all transferors of 1-to-4 unit dwellings of conventional wood 
frame construction must deliver to the purchaser a copy of the homeowners guide to earthquake 
preparedness. The transferor is required to complete the earthquake hazards disclosure part of the 
guide. This legislation is intended to identify such hazards as unanchored (i.e., unbolted) foundation 
plates, unbraced cripple walls, and inadequately anchored water heaters. 



42 



NORTH COAST SCENARIO 




Photo B-2 

The front door was at the top of the stairs before 
this Ferndale house was shaken off its foundation. 
Photo by Kevin Bayliss. 



In the 1969 Santa Rosa earthquakes (M5.6, M5.7), the dollar losses to dwellings was placed at $4 
million (1969 dollars). At the time, dwellings in Santa Rosa were generally one-story and two-story 
single family detached wood frame structures. The effect of period of construction is shown in 
Table B-3. 

It is clear from Table B-3 that older dwellings suffered heaviest damage. 

"This follows historical patterns and is readily explainable by rot, general deterioration in the 
foundation area, and inadequate bracing by today's standard. Damage was almost equally 
divided between one-story and two-story buildings" (Steinbrugge and others, 1970). 

TABLE B-3 

SIGNIFICANTLY DAMAGED WOOD FRAME DWELLINGS 
IN 1969 SANTA ROSA EARTHQUAKES 



Source: Steinbrugge and others (1970) 



STATUS 


AGE GROUP 


Demolished or probably will be demolished 


PRE- 
1920 


1920- 
1940 


1940- 
1969 


18 
11 


8 
1 






Repairable or demolition questionable at this 
time 


TOTAL 


29 


9 






43 



NORTH COAST SCENARIO 



Where pre-1940 houses have not been retrofitted homelessness will be a problem after the 

earthquake. According to Lagorio (1990): 

"In the 1989 Loma Prieta earthquake, there were over 13,000 displaced persons (with some 
later estimates reaching as high as 20,000) and over 8,000 damaged or destroyed dwelling 
units (including single family homes, apartment buildings, and mobile homes). In the 
Watsonville area alone, approximately 2,000 residences were lost. Over 1 ,000 dwelling 
units were destroyed in Oakland. At the time, in San Francisco it was estimated that it 
would take roughly two years to replace and rebuild the estimated 5,000 housing units lost 
at a cost of about $191 million." 



Accounts of the performance of wood frame buildings in the 1994 Northridge earthquake are also 

very informative: 

"Multi-story (mostly two or three stories) apartment and condominium buildings performed 
poorly compared to single family residences. Both the older non-engineered buildings and 
many newer buildings, especially those with the first level tuck-under parking, suffered 
extensive damage. In many cases the first story partially or completely collapsed. The 
Northridge Meadows Apartment Complex, where 16 inhabitants were crushed in apartments 
that shared the ground floor with tuck-under parking, is an example of a "soft story" 
apartment complex" (EERI, 1994). 

Other Potentially Hazardous Structures 

There are a variety of other hazardous structures. Generally, there are few of these in the planning 
area. These include tilt-up concrete buildings built before the mid-1970s non-ductile concrete frame 
structures built before the mid-1970s, and mobile homes (i.e., manufactured modular housing) of 
any age installed without seismic restraints between the undercarriage and the ground (Photo B-3). 




Photo B-3 Trailer home park in the village of King Salmon, south of Eureka. 



44 



NORTH COAST SCENARIO 

Earthquake problems associated with tilt-up construction can be significant. Probably the most 
common cause of severe damage has been separation between the concrete tilt-up wall panels and 
the roof (Figure B-4). Many tilt-up buildings constructed before the mid-1970s have weak 
connections between walls and roof and between walls and floors. This can lead to collapse of the 
roof and floors and cause the wall panels to fall outward. The consequence of tilt-up building failure 
are both life-safety and economic. These buildings are often found in industrial parks, or are used as 
warehouses or even office buildings, and even one or two-wall failures can shut down entire 
buildings. A great many tilt-up buildings failed during the 1971 San Fernando earthquake. 

Data collected on the performance of 1 7 pre-cast concrete structures used as parking garages 

during the 1 994 Northridge earthquake indicate that: 

"Seven garages suffered partial to almost complete collapse of the parking structure. Two 
others experienced collapse of canopies over walkways leading to the top floors of the 
garages. An additional 1 7 garages, for a total of 34, have been reported to have sustained 
sufficient damage to require repair before they can be reopened. ...Six of the seven parking 
structures that partially collapsed were precast" (EERI, 1994). 




Figure B-4 



Typical pre-1973 tilt-up construction. From Lagorio and others, 1986. 



45 



NORTH COAST SCENARIO 

Structures with non-ductile concrete frames (Figure B-5) may collapse. These are typically old 
reinforced concrete frame structures without modern standards for detailing reinforcement in 
columns, beams, and joints. The strength and stiffness of these structures can degrade rapidly in an 
earthquake, causing serious damage or collapse (Photos B-4 and B-5). The Cypress viaduct, which 
collapsed in Oakland during the Loma Prieta earthquake with a loss of 42 lives, is an example of a 
non-ductile concrete structure which met code requirements when it was built (Photo H-1). 

Several mobile home parks like those destroyed during the 1 994 Northridge earthquake are in the 
planning area. Mobile homes installed without seismic foundation restraints are frequently damaged, 
often severely (Photo B-3). In 27 State of California regulated mobile home parks in San Benito, 
Santa Clara, and Santa Cruz counties, 24 percent of the homes (592 out of 2,434) went down 
during the Loma Prieta earthquake. In Santa Cruz County many parks had over 50 percent of their 
homes go down. Interestingly, there were no failures in state regulated parks, where the homes 
had properly installed state approved seismic restraints. 

Tsunamis and Buildings 

It is beyond the scope of this report to predict tsunami damage to buildings, but we offer some 
general information. Single story buildings such as wood frame structures, mobile homes, and light 
weight steel frame buildings are highly susceptible to tsunami damage. The flow of water into 




Figure B-5 



Typical non-ductile concrete frame. From Lagorio and others, 1986. 



46 



NORTH COAST SCENARIO 




Photo B-4 This non-ductile concrete parking structure suffered severe damage and partially collapsed in 

the 1987 Whittier earthquake. This type of construction is a collapse hazard under strong 
shaking. Photo by Ronald Gallagher. 




Photo B-5 Close-up of the parking structure showing structural failure of the non-ductile concrete 

columns. Photo by Ronald Gallagher. 



47 



NORTH COAST SCENARIO 

structures will damage or destroy building contents (e.g., merchandise, equipment, furnishings, 

records, etc.). During the 1964 tsunami: 

"In Crescent City there were ten fatalities due to drowning. In the early hours of the 
disaster twelve people were hospitalized and twelve others were treated as outpatients. 
These numbers do not include the injuries sustained in the clean-up. The port facilities and 
29 city blocks containing 172 businesses, twelve house trailers, and 91 homes were 
damaged or particularly hard hit and eight of the fatalities occurred there. Twenty one boats 
were sunk, due in part to being moored at both ends. ...A fire started at Nichols Pontiac and 
houses on the lower end of town floated off their foundations. ...The third and particularly 
the fourth waves picked up logs, cars, trucks, and other debris which acted as battering 
rams against buildings. One log penetrated the post office. The mail was sucked out but 
later most of it was painstakingly recovered. Fallen electric wires posed additional hazards 
and at least one person was burned by contact with wires while in the water" (Lander and 
others, 1993). 

For thorough and definitive descriptions of tsunamis affecting the west coast of the United States 
refer to Lander and others (1993), or for a complete listing of all United States tsunamis refer to 
Lander and Lockridge (1989). 

Planning Considerations 

Response planners should verify and be knowledgeable of the URM buildings in their jurisdictions 
and develop appropriate contingency plans. A review of the performance of URM buildings during 
the 1 989 Loma Prieta earthquake, particularly in Santa Cruz, Watsonville, and San Francisco's south 
of Market District, will be helpful. 

Damage to pre 1 940 wood frame dwellings and mobile homes will result in the need for shelters 
after the earthquake. Likewise, survivors of the tsunami on Samoa Peninsula and Crescent City will 
be homeless. A review of emergency housing needs after the 1 989 Loma Prieta, 1 992 Petrolia, and 
1 994 Northridge earthquakes will offer valuable insights for planners. 

A shortage of equipment, supplies, food, drinking water, and other necessities will result after the 
earthquake. 

Most of the larger governmental agencies and private corporations now have disaster response plans 
that include pre-arrangements with outside contractors for priority use of temporarily leased 
equipment during the post-earthquake recovery period (e.g., earth moving and other heavy 
construction equipment). In each case, the agency or corporation has stated that it expects the 
outside contractor to supply the required equipment on demand following an earthquake. Response 
planners should verify that their own outside suppliers do not have conflicting contract agreements 



48 



NORTH COAST SCENARIO 

with other agencies or corporations that, in effect, will cause "overbookings" during emergency 
periods. 

Pelican Bav State Prison 

The Pelican Bay State Prison is one of the largest maximum security prisons in the world. It is a 
multi-building reinforced concrete complex. It is about 8 miles (13 km) north of Crescent City, near 
Fort Dick and west of Highway 101 . In this scenario, the prison is within an MMI VIII + area, 
meaning that it will be shaken strongly. The prison is not located within the tsunami inundation 
area, nor is it expected to suffer damage from liquefaction. 

No field survey or engineering analyses were conducted for the prison for this scenario. For 
emergency planning it should be assumed that at least nonstructural damage will occur, such as to 
utility services, interior elements, furnishings, and security systems. For example, damage in the 
1971 earthquake to the juvenile detention center in San Fernando created several problems. They 
included the escape of inmates through an opening created by the partial failure of a yard perimeter 
wall; severe damage to interior walls, floors, and utility services due to the shaking and ground 
failure at the site. The loss of power to electric door locks and related security features made it 
difficult to open doors to release inmates from damaged buildings. Evacuation was hampered by 
barred windows which had to be pried or pulled off. Major damage to a Nicaragua maximum 
security prison following the 1 972 Managua earthquake led to large scale escapes, a riot, and a gun 
battle between military forces and the inmates who were able to secure weapons from the guards 
and arms lockers. 

Planning Scenario 

While it is beyond the scope of this general planning scenario to identify specific buildings that could 
be damaged by this postulated event, a few general guidelines can be provided. 

Unreinforced masonry buildings such as those in the older area of downtown Eureka and Areata, will 
suffer severe to total damage. 

Pre-1940 wood frame structures with cripple walls or unbraced post and pier foundations and those 
not tied down to their foundations will suffer the greatest losses. 

Unrestrained mobile homes will be knocked from their foundations, causing fires from broken gas 
connectors. Mobile homes located in the tsunami run-up areas, will be knocked off their mountings 
by the force of the water. 

49 



NORTH COAST SCENARIO 

Concrete tilt-up buildings, commonly located in newer light industrial and commercial areas, could 
experience severe damage. Often, this is due to inadequate connections between the roof 
diaphragm and the walls. 

In general, it is damage to the area's building stock that creates the greatest long term recovery 
problems. Typical problems include temporary housing for displaced residents, closure of damaged 
commercial structures, loss of employment, loss of tax income to area governments and similar 
problems. 



50 



NORTH COAST SCENARIO 

PUBLIC HIGH SCHOOLS AND COLLEGES 

General Characteristics 

According to data on the seismic performance of public education facilities throughout the State, 
public schools are normally found in a safe condition after an earthquake. Thus, because of their 
large sites, availability of ample parking spaces, cafeterias, gymnasiums, and other amenities, 
schools have strong potential to serve as a critical resource during the earthquake recovery period 
for mass shelter and feeding whenever homes are destroyed or otherwise rendered uninhabitable. 

Because of the emphasis on the earthquake-resistant design of public school buildings in California 

ever since the 1933 Long Beach earthquake (M6.3), a wealth of information exists on the seismic 

performance of public school facilities. Among the many sources of data available, the following are 

especially pertinent: 

"California Public School Directory," 1993 Edition, California Department of Education, 
Sacramento, CA, 1993. 

"Unacceptable Risk: Earthquake Hazard Reduction in One East Bay School District," A. 
Chakos and S.K. Nathe, California State University, Hayward, CA, 1992. 

"Performance of Public Schools in Loma Prieta Earthquake of October 17, 1989," J.F. 
Meehan, Office of the State Architect (OSA), Sacramento, CA, 1990. 

"School Report - The Performance of Public School Plants During the San Fernando 
Earthquake," D.K. Jephcott and D.E. Hudson, Center for Research on the Prevention of 
Natural Disasters, California Institute of Technology, Pasadena, CA, September 1 974. 

"Loma Prieta Earthquake Reconnaissance Report" (EERI, 1990). 

"Northridge Earthquake, January 17, 1994, Preliminary Reconnaissance Report" (EERI, 
1994). 

Engineering and planning consultants have developed extensive technical knowledge and experience 
in the seismic performance of public schools. We made general site location reviews of selected 
public high schools. 

Maps SHM-1 and SHM-2 show the location of public high schools and colleges in the planning area. 
Public elementary schools, middle schools, and private schools are not shown. This chapter is 
applicable to schools of all class levels including institutions of higher education and private schools 
designed and constructed to Field Act standards. Table PS-1 lists the high schools, continuation 
schools, and colleges in the planning area. 



51 



NORTH COAST SCENARIO 



TABLE PS-1 

PUBLIC HIGH SCHOOLS & COLLEGES 
HUMBOLDT AND DEL NORTE COUNTIES 



COUNTY 


SCHOOLS/COLLEGE 


SITE LOCATION 
MM INTENSITY 


Humboldt 


Eureka Senior High 
Areata High 
McKinleyville High 
Zoe Barnum*, Eureka 
Fortuna High 
Ferndale High 
College of the Redwoods 
Cal. State Univ., Humboldt 


VIII + 
VIII + 
VIII -t- 

VIII + 

IX 

IX 
VIII + 
VIII + 


Del Norte 


Del Norte High, Crescent City 
Sunset*, Crescent City 


VIII + 

VIII + 



* Continuation School 



Seismic Considerations 

As mentioned, public schools in California have receiv3d special legislative attention through the 
Field Act with respect to seismic safety following the 1 933 Long Beach earthquake. Over the 
years, the Field Act has been successfully implemented by the Division of the State Architect 
through strictly enforced design and construction practices. 

In the 60 years that have followed, the seismic design provisions of building codes, including those 
for school buildings, have been consistently improved. For example, our report issued in 1987 
concerning an earthquake planning scenario for a M7.5 earthquake on the Hay ward fault in the San 
Francisco Bay Area states that: 

"Looking back in time, it is fair to say that some of the Field Act Schools of 50 years 
ago would not comply with today's Field Act requirements, and indeed could not be 
built today without including significant improvements. While the overall 
performance of public schools will continue to be excellent, it is unreal to expect 
perfection, particularly in view of the large number of public schools in the near 
vicinity of the Hayward fault" (Steinbrugge and others, 1987). 



52 



NORTH COAST SCENARIO 



The same report also states: 

"Public Schools constructed under the Field Act have performed excellently in all 
earthquakes. The performance of public schools has been far better than that for 
other buildings using similar construction materials, but this performance has not 
been perfect. For example, structural damage occurred to buildings at Arvin High 
School in the 1952 Kern County earthquake (M7.7). Structural damage also 
occurred in the West Hills Community College in Coalinga as a result of the 1 983 
Coalinga earthquake (M6.5) (Meehan, 1983). In no case was there a major life 
hazard, and costs of repair were a small fraction of the building's value. Experience 
shows that damage can occur to Field Act schools, and these buildings will not be 
useable until repairs are completed." 



Reports issued on the seismic performance of public schools during the 1989 Loma Prieta 
earthquake (M7.0) again revealed that school facilities designed under the Field Act on the whole 
performed very well. Damage inspection conducted after the earthquake revealed the following: 

1 . "There was only minor structural damage to most public school buildings from the near 
field effects of the Loma Prieta earthquake. A preliminary survey of 1,544 public schools 
in the earthquake-affected region reveals an estimated $81 million in damage. Only five 
schools sustained severe damage. 

Fortunately, the Loma Prieta earthquake occurred after normal school hours. Hazards 
from unbraced and unanchored nonstructural items were evident in many school 
buildings. The following significant hazards continue to constitute a danger to classroom 
occupants during an earthquake: pendant-mounted light fixtures without safety cables; 
suspended acoustical ceiling systems installed without bracing or perimeter wires along 
with their unattached air-conditioning grilles; light lenses, and light fixtures; unanchored 
four-drawer file cabinets, unanchored shelving, and their contents" (EERI, 1990). 

2. "Several school buildings in the area affected by the earthquake were constructed prior 
to the enactment of the Field Act. These buildings had been subsequently strengthened 
or retrofitted to meet building regulations which were less stringent than current building 
standards. The three-story Branciforte Elementary School in Santa Cruz was built about 
75 years ago, well before the Field Act. This building was retrofitted in 1 956. The 
structural system performed very well, but plaster fell in several locations where the 
plaster was supported by wood lath backing. Wood lath is no longer permitted in new 
construction and must be removed when public school rehabilitation projects are 
undertaken. Soquel Elementary School is about 50 years old and was constructed during 
the early years of the Field Act. This building also had plaster fall from old wool lath 
back. A heating radiator also fell off the wall. 

Watsonville High School's main building was constructed in 1917, prior to the 
Field Act; and some rehabilitation work was done in 1935. This building 
experienced extensive plaster damage where plaster was installed over wood 
lath. This building suffered damage to the heavy Spanish roof tile and large 
window glass areas. While the building was being surveyed to determine the 
extent of earthquake damage, it was learned that there were other structural 
deficiencies which will require correction or may lead to eventual 
abandonment of the building. 

After the earthquake, eighty-nine school buildings were investigated and found 
acceptable for operation as emergency shelters for people who had been displaced from 
their earthquake damaged homes. Many of these school buildings were used as shelters 
for several weeks after the earthquake. 

53 



NORTH COAST SCENARIO 



Building codes have undergone significant changes based on recorded evidence from 
earthquakes in the last 20 years. Also, the construction industry has seen many changes 
in the use of the building materials since 1933. It would be prudent to examine all school 
buildings constructed or retrofitted during the early days of the Field Act. These 
buildings need to be examined to determine if they possess the necessary design and 
material strength and stiffness to perform adequately in future earthquakes or if the lack 
of proper maintenance or deterioration has reduced their strength" (Meehan, 1990). 

As observed after the 1 989 Loma Prieta earthquake, pre-Field Act buildings that were retrofitted 
between 1 933 and the 1 960s remain the most likely buildings to suffer structural damage. The 
seismic-resistant upgrade of these buildings focused on structural standards that were different and 
often less stringent than current requirements. 

Owing to the high accelerations experienced in some areas during the 1 994 Northridge earthquake 

(M6.7), general damage to public schools was heavier than anticipated. However, most of the 

damage was nonstructural. Structural damage to schools was not a major factor, e.g., there were 

no structural collapses. Accounts by the Division of the State Architect note that: 

"A total of 22 structures were rated unsafe (Red Tag). However, further review revealed 
that, with the exception of the portable buildings, and some of the lunch centers, most 
structures tagged Red were not in danger of collapse. ...The most important damage 
consisted of wood roof beams slipping off seats because of connection failures aggravated 
by dry rot (e.g., wood decay), as well as effects from pounding with adjacent structures. 

Some permanent buildings such as classrooms, gymnasiums, and administration buildings 
also experienced structural damage; most of these were constructed to pre- 1971 building 
regulations. Potentially hazardous spading of concrete and masonry, up to 5 pounds 
maximum weight per piece, occurred at localized areas on the outside of some buildings. 
Other damage included buckling of diagonal bracing rods, diagonal cracking of shear walls, 
concrete-column joint spalling, and ground cracking extending into buildings. 

The Los Angeles Unified School District, which encompasses the entire city of Los Angeles, 
reported on Sunday, Jan. 23, that about 300 of roughly 800 campuses had sustained some 
damage, but fewer than 100 were not scheduled to open the following Tuesday. The 
district estimated total damage (structural and nonstructural) at $700 million. The schools 
hardest hit were in the portion of the San Fernando Valley west of the I-405 freeway, 
including Northridge, Granada Hills, and Encino. ...Schools in the central and east valley as 
well as in the remainder of the district experienced relatively minor damage. Hamilton High 
School, a URM in West Los Angeles that was built in 1931 and retrofitted after major 
damage in the 1971 earthquake, performed well despite damage to some exterior ornaments 
and pedestrian bridges between buildings. Similarly, a school located blocks away from the 
Santa Monica Freeway (1-10) collapse performed very well with nonstructural damage only" 
(EERI, 1994). 



Planning Considerations 

Almost all non-Field Act public schools are gone. Some private schools, however, still pose an 
earthquake hazard. By definition, therefore, all public school buildings in the study area have been 



54 



NORTH COAST SCENARIO 

designed to meet earthquake resistant design provisions required by the Field Act. 

The Field Act covers public schools and community colleges. Private schools and state institutions 
of higher education generally have built their new buildings in conformance to the technical 
provisions which supplement the Field Act and have upgraded and strengthened some of their older 
existing buildings. Some old buildings still remain in use for purposes other than classrooms. 

The high schools and colleges will experience MMI VIII + or IX ground shaking resulting in 
nonstructural and some structural damage (Table PS-1). 

Underground utility service lines that cross the Little Salmon fault near College of the Redwoods or 
areas of poor ground will be ruptured. As a result, some schools will have functional impairments 
even if their structures remain undamaged by the postulated earthquake. 

California State University, Humboldt is one of the system's older campuses. It is slightly north of 
Areata adjacent to Highway 101 on a steeply sloping site. The campus contains numerous buildings 
varying in age, type of construction, size, occupancy, and seismic resistance. Some earthquake 
rehabilitation projects have been undertaken on the campus and others are yet to be done. Further 
information can be obtained from the California State University's main offices in Long Beach, which 
is currently assessing the seismic performance of all California State University buildings. 

The College of the Redwoods is new enough to have been built under the requirements of the Field 
Act, and no significant structural damage is expected there from shaking. However, significant 
damage will occur because it is adjacent to the Little Salmon fault which will rupture in this 
scenario. Also, transportation and utility services will be interrupted where such systems traverse 
the fault. 

Planning Scenario 

Because of their size, location, and service facilities, public schools are desirable as evacuation 
shelters and mass feeding areas for victims of the earthquake. They will be a critical resource, 
wherever damage to the existing housing stock is severe. 

All wood-frame public schools are expected to survive without structural damage. These are mostly 
one-story elementary schools and high schools with one-story "open planning and exterior 
courtyards" (also referred to as the "open wing configuration") surrounding the classrooms and 
other facilities. There will be some functional restrictions owing to disrupted utility services, broken 



55 



NORTH COAST SCENARIO 

windows, fallen ceiling tiles, jammed doors, and other similar nonstructural effects to 1 percent of 
the classrooms. Typical damage will impair school functions for 2 to 7 days. 

Contingency planners must identify the locations of pre-Field Act school buildings and Field Act 
buildings that were retrofitted between 1 933 and the early 1 960s. Professional damage 
assessments of all such facilities by engineers and architects will be required during the immediate 
post-earthquake period. We assume that damage to 25 percent of such retrofitted and strengthened 
schools buildings will occur. Evidence of structural damage will delay re-occupancy on a long-term 
basis. 

Public school structures that are two or more stories high are often designed with construction 
systems that use reinforced concrete or other unit masonry wall materials. After the earthquake, 
these also will need to be inspected. If any significant cracking is found, occupancy will be delayed 
for repairs. The inspection will take from 2 to 3 days depending on the availability of inspectors, 
with repair taking up to several weeks depending on the extent of damage. 

Immediately following the earthquake, road interruptions and closures could make local access to 
school sites a serious problem for school administrators and emergency response personnel. 
Alternative routes to reach schools with potential access problems must be established. In areas of 
expected high intensity ground shaking, contingency plans must include care for students for up to 
1 hours after the event. 



56 



NORTH COAST SCENARIO 

HOSPITALS 
General Characteristics 

When setting priorities among the many demands to be taken into consideration during the 
earthquake recovery period, the disaster response planner must give highest priority to saving lives 
and treating casualties. Hospital buildings, classified as critical emergency facilities, and the 
provision of acute health services are obviously vital in this regard. Staff personnel and medical 
resources, including medical supplies and equipment on-site and in warehouses and/or distribution 
centers, blood banks, ambulance services, clinical laboratories at hospitals, and other related critical 
elements of the medical system must be ready and available. 

A major general acute care hospital provides specific medical services and includes an emergency 
room with facilities for intensive care, and surgery. Table H-1 lists all of the principal hospitals. 
These were surveyed in the field and reviewed for potential earthquake effects. Maps SHM-1 and 
SHM-2 show their locations in Humboldt and Del Norte counties. One small hospital (15 beds) is in 
Garberville at the southern end of Humboldt County. It was not visited during the preparation of 
this planning scenario. 

For a complete inventory of all types of medical facilities in the planning area and throughout 
California, refer to the "Health Facilities Directory, July 1992," issued by the Licensing and 
Certification Division, California Department of Health Services. 

A large percentage of the new major hospitals constructed in the state under the seismic 
performance standards established by the Hospital Seismic Safety Act of 1 973 incorporated specific 
types of structural design, and many are composed of building configurations limited to four or five 
stories. These general building characteristics will be common to future hospitals constructed in the 
planning area. The implications of the planning and construction of medical facilities designed under 
the 1 973 Hospital Act are described below in the Seismic Considerations and Planning 
Considerations sections which follow. 

Seismic Considerations 

The operational capacity and functional continuity of medical facilities are critically dependent on 
utility lifeline support systems (e.g., water supply, electric power, waste water disposal) and 
communication/transportation networks. This dependency on lifeline systems and the complexities 



57 



NORTH COAST SCENARIO 

TABLE H-1 
PRINCIPAL HOSPITALS IN HUMBOLDT AND DEL NORTE COUNTIES 









NO. 


SITE LOCATION 


DATE 






HOSPITAL 


CITY 


COUNTY 


BEOS 


MM INTENSITY 


BUILT 


ADDITION 


Redwood Memorial 


Fortuna 


Humboldt 


49 


IX 


1929 


1955 & 1976 


St. Joseph's 


Eureka 


Humboldt 


92 


VIII + 


1972 


1990 


General 


Eureka 


Humboldt 


83 


VIII + 


1965 


1993 


Mad River Community 


Areata 


Humboldt 


78 


IX 


1955 


— 


Sutter Coast 


Crescent City 


Del Norte 


46 


VIII + 


1992 


— 


TOTAL 






348 









found in components of hospital buildings make them vulnerable to disruptions and impairments 
including those commonly caused by major earthquakes: 

1 . Structural damage 

2. Nonstructural damage 

3. Failure of utility lifeline support systems 

4. Damage to critical supplies, contents, and equipment 

5. Accessibility of ambulances and emergency service vehicles to and from the site 

6. Fire following earthquake 

Hospitals built to the standards of the 1 973 Hospital Act should perform well in a strong 
earthquake, particularly in comparison to ordinary buildings. Hospitals built in the 1950s and 1960s 
did not have the same amount of seismic resistance, and did not have the damage control features 
of those constructed under the 1 973 Hospital Act. The Act also requires seismic design of 
equipment, nonstructural building components, and architectural elements. Before 1973, there were 
few or no such requirements. Currently, items such as emergency generators, battery racks, critical 
equipment, and large medical apparatus, for example, must be secured against sliding or 
overturning. This greatly increases the likelihood of the post-earthquake availability of medical 
facilities for the treatment of casualties and other emergency services. 

During the aftermath of the 1971 San Fernando earthquake (M6.7) which caused significant damage 
to four major medical facilities (Indian Hills Medical Center in Los Angeles, Holy Cross Hospital in Los 
Angeles, Veterans Administration (VA) Hospital in Los Angeles County, and Olive View Hospital in 
Sylmar) the State of California adopted the Hospital Seismic Safety Act of 1973. This required 
higher seismic performance standards for hospital buildings than those required for ordinary 



58 



NORTH COAST SCENARIO 

buildings, to protect occupants from injury as well as to protect the functionality of hospitals. In the 

1994 Northridge earthquake (M6.7) however, new and old hospitals were functionally impaired: 

"Nonstructural damage itself caused the temporary closure, evacuation, or patient 
transfer of Olive View Medical Center (the 1 980s replacement hospital for the facility 
damaged in 1971), Holy Cross (a replacement for the original Holy Cross), Indian Hilts 
(the same building that experienced the 1971 earthquake), and the Sepulveda VA 
Medical Center (in existence at the time of the San Fernando earthquake and distinct 
from the Sylmar VA facility where buildings collapsed in 1971). (The closure of St. 
John's Hospital in Santa Monica, although it suffered major nonstructural damage, was 
attributable to structural damage.) 

Major nonstructural element damage (heating, venting, air conditioning and piping) 
occurred in mechanical penthouses, and the penthouses themselves were severely 
damaged in some instances. In several facilities, large in-line supply fans were thrown 
through the exterior walls of the penthouse. The penthouses were often angle braced 
frames with no columns at one end to brace; thus, severe buckling failures occurred 
when overloaded. 

The most severe damage to healthcare facilities occurred in the Santa Monica area 
where a total of seven red tags were issued to five facilities. Four other red tags were 
issued to buildings in Los Angeles, and one more in San Pedro. Except for one 
warehouse, all the red tagged buildings were for patient care. Many of the red tags 
were issued because of severe diagonal cracking in concrete shear walls. Cracking 
extended through the entire thickness of those walls. Another red tagged building was 
evacuated because of the potential loss of vertical support capability resulting from 
column damage" (EERI, 1994). 

A publication issued after the 1 994 Northridge earthquake by the Central United States Earthquake 

Consortium (CUSEC) indicates that: 

"The Northridge earthquake is the most destructive earthquake in the U.S. since the 
1906 San Francisco earthquake (M8.0). Direct economic losses are estimated currently 
at over $20 billion. ...One of the top priorities after the earthquake was an assessment 
of the damages to hospitals and Emergency Medical Service (EMS) System. These 
assessments were undertaken by local government (public health, emergency medical 
services, and emergency management), the State of California, and local officials in the 
Central States." 

Table H-2 depicts the range of damages to hospitals in the Northridge/Los Angeles area, listed under 
five categories of damage and ability to function. 

After the 1989 Loma Prieta earthquake (M7.0), an assessment report was issued by the Office of 
the California State Architect (OSA) on 1 7 hospitals in the East Bay and South Bay counties of the 
San Francisco Bay Area. Out of the total of 17 buildings inspected, five had no building damage, 
five had nonstructural damage but no structural damage, six had minor structural damage, and one 
had structural damage to an old tower wing built in 1 927 "considered serious enough to 
compromise its capability to withstand another earthquake." The nonstructural damage reported by 
the five hospitals was generally limited to damaged elevators, equipment anchorage and pipe 

59 



NORTH COAST SCENARIO 

TABLE H-2 
NORTHRIDGE EARTHQUAKE - INITIAL IMPACT ON AREA HOSPITALS 



CATEGORIES* 


HOSPITAL 


EPICENTER" 
DISTANCE 


DESCRIPTION 


1 


Olive View 


>30 


Evacuate 377 patients 


1 


Granada Hills 


>10 


Serious water damage, no communications, needs to 
evacuate 


1 


VA Sepulveda 


>10 


Evacuate 300 patients to Long Beach VA Hospital 


1 


Holy Cross 


>10 


Diverting ambulance patients, water leaks, will evacuate 
17 ICU patients 


2 


Northridge Community 


>10 


Evacuate 23 neonatal patients, emergency services only 


3 


Kaiser/Pasadena 


>10 


Significant interior damage, unable to accept new patients 

via ambulance 


3 


Santa Monica 


>30 


Unable to accept new patients via ambulance 


3 


Simi Valley 


>10 


Unable to accept new patients via ambulance 


4 


St. Joseph's/Burbank 


>30 


Minor water damage 


4 


Henry Mayo/ Newhall 


>30 




4 


Valley Presbyterian 


>10 


No heating, venting, air conditioning 


4 


Encino 


>10 


Plaster cracking 


4 


Kaiser/Woodland Hills 


>10 


Minor nonstructural cracking 


4 


Kaiser/West L.A. 


>30 


No significant damage 


4 


Humana 


>10 


No water or emergency power 


4 


Pacifica 


>30 


Possible evacuation, no water or emergency power 


4 


Thompson Memorial 


>30 


Pipes loose 


4 


Glendale Adventist Memorial 


>30 


Minor cracks to interior 


4 


Huntington Memorial 


>30 


Elevator service out 


4 


Kaiser/L.A. 


>30 


Concrete spading on adjacent parking structure 


4 


Cedars Sinai 


>30 


Expansion joint damage 


4 


St. Luke Medical 


>30 


Minor plaster cracking 


4 


Sherman Oaks 


>10 


Water pipes broken 


4 


Valley Hospital 


>10 


Minor water damage 


4 


Verdugo Hills 


>30 


Minor spalling/surface wall cracks 


4 


AMI Tarzana Regional 


>10 


Minor plaster cracking 


5 


Newhall Community 


>30 


Needs generator 



'Status Categories: 1 
2 
3 
4 
5 



Total major evacuation 

Partial evacuation 

Unable to accept new patients 

Damaged but functional 

Need help to remain operational 



In miles 
Source: THE CUSEC JOURNAL, vol. 2, no. 1, chart 1. p. 



60 



NORTH COAST SCENARIO 

support damage, spalling and buckling at seismic joints, failure of vertical fan anchorage at roof level 
and minor cracks at ceilings and walls. 

In the 1992 Petrolia earthquake "Preliminary observations by the USGS indicates that there were 
approximately six to seven miles of the Humboldt Coast that experienced a seismic uplift of one-half 
to one meter" (EERI, 1992a). One hospital in Fortuna, 15 miles (24 km) from the coastline, was 
the closest to the epicentral region of the 1992 Petrolia earthquake (M7.0), 30 miles (50 km) away. 
Typical nonstructural building damage was reported. 

Planning Considerations 

Hospitals close to surface fault rupture can be seriously affected by unusually strong shaking, by 
disruption of utilities, and by access problems. All hospitals in Humboldt and Del Norte counties 
will be within 7 to 12 miles (12 to 20 km) from the CSZ fault surface that dips eastward. 

Hospitals not constructed to the standards of the 1 973 Hospital Seismic Safety Act can be seriously 
damaged, even at some distance from the fault. In addition, those hospitals with unanchored 
emergency equipment (e.g., generators, battery racks) and with unsecured medical apparatus (e.g., 
laboratory equipment) can suffer serious impairment of operations. 

In studying the post-earthquake operational capabilities of hospital facilities, planners should review 
the following: 

1 . Physical damage to buildings 

2. Loss of life and injuries to personnel and patients 

3. Loss of medical supplies and equipment 

4. Loss of hospital functions from disrupted utilities and access 

Because of the rural nature of Humboldt and Del Norte counties, getting the injured to hospitals may 
be difficult. If a local hospital is closed by earthquake damage, except for the two in Eureka, travel 
to the next closest hospital may involve distances of over 20 miles (32 km) on possibly damaged 
and congested roads. Much greater distances would be involved for residents of Del Norte County. 
Helicopter evacuation of the injured will be needed. 

Planning Scenario 

Roads and bridges will be damaged, and travel on them will be difficult or blocked. Utilities crossing 
the Little Salmon fault will be severed and out of service. 



61 



NORTH COAST SCENARIO 

We assume that all five hospitals may have water outages for 3 days and power outages for 2 days 
(Table H-1). For planning purposes, we also assume that a medical facility constructed before 
enactment of the 1973 legislation will be disabled. We also assume that hospital facilities 
constructed since the Hospital Act of 1 973 will remain functional. 

While there are five hospitals in the main impact area, their combined bed capacity is comparatively 
small. This limited capacity plus the possibilities of damage, loss of utility services, disruption of 
roads, and the long distance to any other comparable facility, means that some of the most 
seriously injured may have to be evacuated by air to outlying locations. Planners should assume 
that victims and their relatives will converge on hospital facilities, whether they are operational or 
not. 

Emergency response planners should note the locations of large acute health care facilities 
elsewhere in nearby counties. Planners also must realize the limited availability of overland routes 
(refer to Highways chapter), and provide helicopters or other means to move overflow casualties. 

One of the hospitals has a portion built before 1972. It will be susceptible to damage from the 
scenario earthquake. Another hospital is composed of a set of one story wood frame buildings. It is 
a trauma center and was built according to the requirements of the Hospital Seismic Safety Act. 
While the buildings are expected to perform well, it is in an area moderate to low potential for 
liquefaction. 

One way of examining the potential loss of facilities is to estimate hospital bed loss rather than 
building damage. A slightly damaged building evacuated for psychological or liability reasons will 
result in a critical loss of hospitals beds, just as it would for severe structural damage. For response 
planning purposes, we anticipate that out of 348 beds in the five hospitals, 1 1 9 (34 percent) will be 
unavailable for treatment of earthquake related casualties. As shown in the 1 989 Loma Prieta 
earthquake and others, severe non-structural building damage to hospital facilities also will lead to 
loss of bed capacity. Up to 50 percent of the beds will be unavailable where ground shaking 
intensities of MMI IX are postulated, and 30 percent will be lost in the MMI VIM + areas. 



62 



TRANSPORTATION LIFELINES 



SCENARIO MAPS AND DAMAGE ASSESSMENTS 

ARE INTENDED FOR EMERGENCY PLANNING 

PURPOSES ONLY 



THEY ARE BASED ON THE FOLLOWING HYPOTHETICAL 
CHAIN OF EVENTS: 

1 . A PARTICULAR EARTHQUAKE OCCURS 

2. VARIOUS LOCALITIES IN THE PLANNING AREA 
EXPERIENCE A SPECIFIC TYPE OF SHAKING OR 
GROUND FAILURE 

3. CERTAIN CRITICAL FACILITIES UNDERGO DAMAGE AND 
OTHERS DO NOT 

THE CONCLUSIONS REGARDING THE PERFORMANCE OF 
FACILITIES ARE HYPOTHETICAL AND AND NOT TO BE 
CONSTRUED AS SITE-SPECIFIC ENGINEERING EVALUATIONS. 
FOR THE MOST PART, DAMAGE ASSESSMENTS ARE STRONGLY 
INFLUENCED BY THE SEISMIC INTENSITY DISTRIBUTION MAP 
DEVELOPED FOR THIS PARTICULAR SCENARIO EARTHQUAKE. 
THERE IS DISAGREEMENT AMONG INVESTIGATORS AS TO 
THE MOST REALISTIC MODEL FOR PREDICTING SEISMIC 
INTENSITY DISTRIBUTION. NONE HAVE BEEN FULLY TESTED 
AND EACH WOULD YIELD A DIFFERENT EARTHQUAKE 
PLANNING SCENARIO. FACILITIES THAT ARE PARTICULARLY 
SENSITIVE TO EMERGENCY RESPONSE WILL REQUIRE A 
DETAILED GEOTECHNICAL STUDY. 

THE DAMAGE ASSESSMENTS ARE BASED ON THIS SPECIFIC 
SCENARIO. AN EARTHQUAKE OF SIGNIFICANTLY DIFFERENT 
MAGNITUDE ON THIS OR ANY ONE OF MANY OTHER FAULTS 
IN THE PLANNING AREA WILL RESULT IN A MARKEDLY 
DIFFERENT PATTERN OF DAMAGE. 



NORTH COAST SCENARIO 

HIGHWAYS 
General Characteristics 

The California Department of Transportation (Caltrans) was created in 1 972 and is one of the 
leading organizations committed to the seismic design and research of highway bridges. Caltrans, 
which contributed to this chapter, is based in Sacramento and operates out of 1 2 district offices and 
has over 300 maintenance stations throughout the state. 

This earthquake planning scenario considers the portion of the state highway system in Caltrans 
District 1 , including over 250 structures on 1 2 state highway routes. 

Seismic Considerations 

The only identified fault crossing is Route 101 across the Little Salmon fault which will slip in 
conjunction with the M8.4 event. A Federal Highway Administration study (U.S. Department of 
Transportation, 1 982) considers that normally those areas having MMI greater than VII will have 
significant damage to highway structures. The damaging effects from ground failure also must be 
considered independently in making performance assessments. 

As a result of the 1971 San Fernando earthquake (M6.7), Caltrans implemented design criteria and 
details for bridges that improved seismic resistance. The most significant damage will occur in 
structures designed between 1946 and 1971 that have not yet been retrofitted. However, a 
legislative mandate following the 1 989 Loma Prieta earthquake (M7), requires that all seismically 
deficient state structures be under contract for retrofit by December 1993. 

The initial Caltrans retrofit program (1971-1985) involved the application of hinge restrainers to 
unrestrained superstructure expansion joints. The subsequent single column retrofit program 
concentrated on increasing the seismic resistance of single column substructures to current 
standards. By July 1992, all but 25 of the 271 single column bridges statewide had been 
advertised for retrofit. The detailed review of as-built plans for all state bridges is completed. The 
current retrofit program is to increase the seismic resistance of deficient bridge structures. Although 
retrofitting is no guarantee against collapse under the most intense shaking, it does improve the 
chances that a structure will survive with repairable damage. Examples of repairable damage 
include the tipping of short rocker bearings, minor cracking of piers and columns, and vertical 
displacements allowing an asphalt patch. Retrofitted structures may be significantly damaged and 
require road closure for repair, but they generally will not collapse. 



63 



NORTH COAST SCENARIO 

Areas of potential liquefaction and seismically induced landslides will impact the highway system. 
The amount of movement due to liquefaction and landslides is erratic and difficult to predict. Most 
effects on the highway system involve blockage by rockfalls, settlement of sediment fills, and 
slumping of soils near streams and other water bodies. 

We reviewed the general characteristics of the structures in light of their historic failure 
mechanisms. In particular, the damage patterns witnessed during the Loma Prieta earthquake were 
used for many of the predictions in this scenario. In some instances damage can occur in MMI VII 
zones far from the epicenter, when soil conditions and the period of a long structure lead to reso- 
nant amplification. Collapse of the Cypress Structure during the Loma Prieta earthquake is the 
classic example (Photo H-1). 




Photo H-1 Collapsed steel rebar and concrete columns of the Cypress I-880 freeway structure, Oakland, 

California. A 1-mile lenght of this double-decked reinforced-concrete viaduct collapsed onto 
commuter traffic during the Loma Prieta earthquake. The failed column in the foreground 
supported the top deck. Built in the 1950s, the columns had vertical steel reinforcing rods but 
lacked the spiral reinforcing rods used in modern construction. Photo by Michael Rymer, 
courtesy of the U.S. Geological Survey. 

Planning Considerations 

Planners need to identify major emergency corridors that will have the least amount of damage in 
the earthquake. The best emergency routes are wide, at grade or on good ground, and should avoid 
adjacent tall buildings and power lines that could be damaged. Utility companies and local 
government agencies need to identify installations and facilities they will need to inspect, repair, 
operate, or access in the emergency. In general, routes that have sections crossing areas of both 
high and moderate liquefaction potential will have outages only in areas designated high liquefaction 



64 



NORTH COAST SCENARIO 

potential on the map. Critical facilities include communication centers, hospitals, airports, heliports, 
staging areas, fuel storage sites, and other locations essential for emergency response operations. 
Highway emergency response plans need to be coordinated with those developed for air and rail. 
Access to and travel through stricken areas will be difficult and will be limited to the highest 
emergency priorities. 

Highway 101 will be unusable in most of Humboldt and Del Norte counties for at least the 3 day 
duration of this scenario and for up to a month later. The bridge between Eureka and the Samoa 
Peninsula will also be unusable. Likewise easterly routes through the mountains (e.g. Routes 36, 
299, 96, and 1 99) will be blocked by landslides and other damage. Planners need to identify access 
routes to communication centers, hospitals, airports, staging areas, fuel storage sites, and other 
locations necessary for emergency response. Highway outages will restrict emergency supplies 
from outside the area for 14 days. 

Highways and Bridges 

Highway 101, the main thoroughfare along the California coast, extends through both Humboldt and 
Del Norte counties. A considerable portion of the highway in southern Humboldt County is inland 
from the coast, mostly notable where the highway follows along the Eel River, and many parts of 
the highway are in slide areas. There are also numerous bridges and overpasses along this highway, 
many of which were constructed before 1971 . Bridges constructed at that time were not as well 
designed for lateral forces as those built in later years. 

After the earthquake that occurred in southern California on February 9, 1971, Caltrans increased 
the seismic coefficient as a function of gravity to a higher level of lateral force design. 
Subsequently, bridges and overpasses were substantially increased in strength to resist lateral forces 
of earthquakes. 

Along Highway 101, especially approaching the City of Fortuna, the land is closer to the Pacific 
Ocean and the wetlands and marshes become prevalent. The possibility of soil liquefaction 
becomes a potential problem for the many bridges and overpasses in these areas. Farther north in 
Eureka, Samoa Peninsula, Areata, and areas between these locations, there are many marshlands 
and wetlands which are also in danger of liquefaction. Highways, bridges, and overpasses in these 
areas are particularly vulnerable to severe damage from liquefaction. 

Highway 101 winds along the coast from Areata to Crescent City through intermittent wetlands and 
marshes. These areas create potential problems for bridges and overpasses, especially where they 



65 



NORTH COAST SCENARIO 

span rivers and streams. Possible tsunami damage to highways is discussed briefly under Damage 
Assessments, although the tsunami runup was modeled only for limited parts of Eureka and 
Crescent City. 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Locations of damage assessments are shown on Map H-1 (for nos. 1 
to 8), Map H-2 (for nos. 9 to 28, and no. 37), and Map H-3 (for nos. 29 to 56). Routes not 
discussed may be assumed to be open with delays due to heavy traffic and obstructions. 

MAP NO . LOCATION 

1 Route 101, Mendocino County Line to Benbow 

MMI VIII- 

Potential for landslides 

Closed for 3 days 

This route was closed as a result of the 1 964 storm. The damage to highway structures 

will be minor, with the blockage to the route being due to reactivation of known 

landslides. Movement of the Reed Mountain slide will block the Eel River to a shallow 

depth, but the highway will be unaffected. A slide north of Benbow Bridge will block 

the road. 

2 Route 101, north of Garberville 
MMI VII 

Potential for landslides 

Restricted for 1 day 

The shaking intensity here will be just enough to reactivate the Bear Buttes landslide. 

The low relief on the ridge above slide suggests it will block the river to a shallow depth 

only. The effect on the road will be minor because the slide is west of river and road is 

east of the river. 

3 Route 101, Eel River Bridge north of Hooker Creek 

MMI VII 
Open 



66 



NORTH COAST SCENARIO 

This is a steel bridge on three concrete piers, with the two southern piers in the inactive 
channel. The northern pier has cable restrainers. 

4 Route 101, Phillipsville to Meyers Flat 
MMI Vlll-to IX 

Potential for landslides 
Moderate potential for liquefaction 
Closed for 3 days 

There will be moderate structure damage and roadway damage from landslides. One 
landslide will block the highway as well as the river. Within 2 days the natural dam 
produced in the river will be close to failure, resulting in the need to evacuate the down- 
stream area. 

5 Route 254, Alternate Route from Phillipsville to Meyers Flat 
MMI IX 

Potential for landslides 

Moderate potential for liquefaction 

Closed for 3 days 

There will be moderate structure damage along this route, and road closure from 

landslides. 

6 Route 254, Alternate Route from Meyers Flat to Jordan Road 

MMI VIII- to IX 

Potential for landslides 

Moderate potential for liquefaction 

Closed for 3 days 

Moderate structure damage similar to the damage that will occur on the parallel portion 

of Route 101. 

7 Route 101, Meyers Flat to Stafford Bridge, and Dyerville Loop Road along the Eel River 

MMI Vlll-to IX 

Potential for landslides 

Moderate potential for liquefaction 

Closed for 3 days 

There will be moderate structure damage along this route. Failure of the concrete 

overpass on Route 101 for the road to Honeydew will block both Route 101 and 

Honeydew Road. One mile south of the Pepperwood exit, several earthflows will 



67 



NORTH COAST SCENARIO 

encroach on Route 101 . There will be minor settlement at the north approach fill to the 
Stafford Bridge. This retrofitted bridge (over South Fork of Eel River) will be damaged. 

8 Secondary roads southwest of Route 101, Shelter Cove to Ferndale (not part of the 
state highway system) 

MMI Vlll-to IX 
Potential for landslides 
Restricted for 3 days 

Numerous landslides will restrict traffic to the small communities of Shelter Cove, 
Honeydew, and Petrolia. As in the 1980 earthquake, steep roadcuts will fail (Kilbourne 
and Saucedo, 1981, Figure 15). In 1992 "Strong ground shaking during the 
earthquakes triggered numerous landslides in steep mountainous areas. The widespread 
landslides blocked or impeded traffic on the limited number of roads that serve this 
rugged region. Tension cracks, due to soil compaction and downhill slumping, restricted 
traffic on the Mattole Road between Honeydew, Petrolia, and Ferndale" (Reagor and 
Brewer, 1992, p. 116). 

9 Route 283, Scotia to Eel River. 
MMI IX 

Closed for 3 days 

This 0.36-mile long segment of Route 283 includes the Eel River crossing. There will be 

major structural damage to the bridge. 

10 Route 101, Rio Dell (Stafford) Bridge northwest to Fortuna 
MMI IX 

Moderate to high liquefaction potential 

Closed for over 3 days 

Due to strong ground shaking, there will be major structural damage to several bridges 

crossing the Eel and the Van Duzen rivers north of Rio Dell. 

1 1 Route 36, Alton to Hydesville 
MMI VIII + 

Open 

No structures will be affected and the surface cracks in the roadway will be small. 



68 



NORTH COAST SCENARIO 

12 Route 36, Hydesville to Bridgeville 
MMI IX 

Moderate potential for liquefaction 

Potential for landslides 

Closed for 3 days 

Fill failures will undermine the road and rock falls will cover it near Grizzly Creek 

Redwood State Park. The structure crossing Yager Creek will have major damage and it 

will take 3 days to provide temporary repairs necessary to carry emergency traffic. In 

other places there will be damage to structures and roadways from ground failure due to 

liquefaction. 

13 Route 36. Bridgeville to Larabee Valley 

MMI VII 

Open 

Minor and repairable structural damage. The old bridge crossing the Van Duzen River at 

Bridgeville was being replaced by a new structure in 1993. Existing slide in melange will 

not reactivate in this event. 

14 Route 36, Larabee Valley to Mad River 
MMI VII to VIII + 

Moderate potential for liquefaction 

Potential for landslides 

Closed for 2 days 

Moderate structure and roadway damage from liquefaction. Pavement cracks and 

separation will occur due to liquefaction. All structure damage can be repaired by using 

temporary shoring methods. 

15 Route 101, Fortuna Over-crossing 
MMI IX 

Moderate potential for liquefaction 

Closed for 3 days 

Due to strong ground shaking, the Fortuna and the Twelfth Street over-crossings will be 

damaged. Alternative city routes in Fortuna will have to be used. 

16 Route 101, northwest Fortuna to Beatrice 
MMI VIII + 

Restricted for 1 2 hours 



69 



NORTH COAST SCENARIO 



There will be only minor structure damage along this route, mostly due to abutment 
settlement. The route will be open, but will have traffic delays for 12 hours. 

17 Route 211, Ferndale to Fernbridge 

MMI IX 

High liquefaction potential 
Closed for 3 days 

This route will have moderate structure damage and pavement separation and 
settlement problems will develop due to liquefaction. The old bridge over the Eel River 
(Photo H-2) will be severely damaged. 




Photo H-2 The old bridge across the Eel River at Fernbridge. 

18 Route 101, Beatrice to Pine Hill 

MMI IX 

High liquefaction potential 
Potential for landslides 
Closed for 3 days 

There will be major structure and roadway damage north of Beatrice and either side of 
Spruce Point due to liquefaction. The landslides on Humboldt Hill east of the freeway 
will be reactivated and will close one of the four lanes. There will be minor damage to 
the southbound bridge across the Elk River near Pine Hill. Many possible detours will be 
available including the parallel bridge. 



70 



NORTH COAST SCENARIO 

19 Route 101, Fields Landing Overhead 

MMI IX 

Little Salmon Fault Rupture 
High liquefaction potential 
Closed for more than 3 days 

Two of the four spans of the Fields Landing Overhead (locally known as Tompkins Hill 
Road Overpass) collapsed in the 1980 M7.0 earthquake (Semans and Zelinski, 1980, 
photos 1 to 38; Kilbourne and Saucedo, 1981, photos 2 to 3). The two spans were 
replaced more or less according to the original design (Photo H-3) and both the old and 
the new spans were retrofitted with hinge restrainers to prevent future support failures. 




Photo H-3 Route 101 Fields Landing Overhead. 

The superstructure has undergone up to 2 inches of progressive lateral movement 
between 1965 and 1980 (Semans and Zelinski, 1980, p. 2). Caltrans now expects this 
structure to perform much better and only suffer minor damage. In 1 980, however, the 
intensity was only VII at Fields Landing (Kilbourne and Saucedo, 1981), whereas the 
scenario event will produce MMI IX with a shaking duration many times what it was in 
1980. The bridge is founded in soft, saturated, sandy sediments and the scenario event 
will produce liquefaction and subsidence of many of the supports. The Little Salmon 
fault traverses the northern approach of the overhead (refer to Wills, 1990 for details). 
Slip along this fault will produce up to 12 feet (4 m) of thrust movement across a zone 
tens of feet wide (Carver, 1993). 



71 



NORTH COAST SCENARIO 

20 Route 101, Pine Hill to Route 255 

MMI VIII + 

Restricted for 1 day 

Highway 101 appears to be on a cut bench in Pleistocene sedimentary deposits. 

Although no large scale failures will occur, the road cuts on the east side of the highway 

in southwest Eureka will fail, closing the north bound lanes. 

21 Route 255 to Samoa 
MMI IX 

High liquefaction potential 
Tsunami inundation zone 
Closed for 3 days 

There will be major damage to the bridges across the Eureka, Middle, and Samoa 
Channel. The above three structures are under contract for special study and retrofit 
design, with the retrofit construction to be completed by 1999. However, the 
approaches and roadways connecting bridges are on shallow fill over mud. These will 
settle, making the bridges inaccessible. The west end of the bridge is in the tsunami 
runup zone. 

22 Route 255. Samoa to Areata 
MMI IX 

High liquefaction potential 

Tsunami inundation zone 

Closed for 3 days 

This route will have moderate structure damage with roadway and pavement separation 

due to lateral spreading induced by liquefaction. The tsunami will block the road with 

debris. 

23 Route 101, Eureka to 255/101 Interchange, Areata 
MMI IX 

High liquefaction potential 

Closed for 3 days 

Moderate damage to structure with roadway and pavement separation due to lateral 

spreading induced by liquefaction. 



72 



NORTH COAST SCENARIO 

24 Route 255/101 Interchange, Areata (Sunny Brae Over-crossing) 
MMI IX 

High liquefaction potential 

Closed for 3 days 

Moderate damage to structure, with roadway and pavement separation due to lateral 

spreading induced by liquefaction. Detours to available surface streets in Areata will be 

necessary. 

25 Route 101 from 101/255 Interchange to 101/299 Interchange 
MMI VIII + to IX 

Restricted for 1 day 

There will be minor structure damage, with detours available for emergency traffic. 

26 Route 101 Bridges and Route 101/200 Interchange north of Areata 
MMI IX 

High liquefaction potential 

Closed for 3 days 

There will be structure damage to the parallel bridges across the Mad River and to the 

roadway interchange. 

27 Route 101 from 101/299 Interchange to 101/200 Interchange 
MMI IX 

High liquefaction potential 

Closed for over 3 days 

There will be major structure damage including abutment cracking and fill settlement at 

the Route 101/299 interchange. This route will have moderate structure damage with 

roadway and pavement separation due to lateral spreading induced by liquefaction. 

28 Route 299 from 101/299 Interchange to Glendale 
MMI IX 

Moderate to high liquefaction potential 

Closed for 3 days 

There will be liquefaction damage to the roadway. 

29 Route 299, Glendale to Blue Lake 
MMI VIII + to IX 

Potential for landslides 



73 



NORTH COAST SCENARIO 

Moderate potential for liquefaction 

Restricted for 2 days 

Despite some preexisting right lateral offset at the east approach-span connection of the 

Mad River Bridge there will be no structure damage. Some existing landslides will be 

reactivated and will block the west-bound lanes and damage the roadway. 

30 Route 299, Blue Lake to Berry Summit 

MMI VIII + 

Closed for 2 days 

This area has many landslides that are too small to show at this map scale, (Carver, 

1 993) suggesting that the route will be closed in many places by small slides. There will 

be moderate structure damage to the bridge crossing the North Fork of the Mad River 

with the bridge being closed for 1 2 hours for repairs. 

31 Route 299, Berry Summit to Salyer 
MMI VII 

Potential for landslides 

Closed for 1 day 

There will be no structure damage. Rock falls and landslides will block the roadway for 

1 day. 

32 Route 299, Salyer to east edge of study area 

MMI VII 

Open with delays 

There will be minor structure cracking and settlement here, but the route will remain 

open, with delays due to rockfalls and small slides. 

33 Route 96. Willow Creek to Orleans 

MMI VII to VIII + 

Potential for landslides 

Closed for 3 days 

There will be major damage to the bridge across the Trinity River, but other structures 

will suffer only moderate, repairable damaged. Only portions of the route will be closed 

for 3 days. Rockfalls will block the roadway for at least 1 day. 



74 



NORTH COAST SCENARIO 

34 Route 169, Weitchpec to Cappell Creek 
MMI VI 

Open with delays 

There will be no structure damage along this route. Rockfalls and small slides will cause 

traffic delays. 

35 Route 169, Cappell Creek to Johnsons 
MMI VII 

Potential for rock falls 

Closed for 1 day 

Although there will be no structure damage, this route will be closed by extensive 

rockfalls that are too small to show on Map S-3 individually. 

36 Route 96, Dillon Mountain 
MMI VII 

High potential for rock falls 

Closed for 2 days 

Moderate structure damage to the Klamath River Bridge and the Dillon Creek Bridge on 

Highway 96, about 1 5 miles (24 km) north of the Siskiyou County line. Rockfalls will 

block portions of this route. 

37 Route 200 from Route 200/101 Interchange to Route 200/299 Interchange 

MMI VII to VIII + 

Closed for more than 3 days 

In addition to major damage to the interchanges with Routes 101 and 299, the roadway 

will be damaged by shaking. 

38 Route 101 from Route 200 to Clam Beach 

MMI VIII + 

Open with delays 

No structure or roadway damage. Tsunami inundation is possible at Clam Beach. 

39 Route 101, at Little River Beach State Park 
MMI IX 

High liquefaction potential 
Closed for 3 days 



75 



NORTH COAST SCENARIO 

There will be major structure damage at Little River Bridge, and liquefaction damage 
along this route. 

40 Route 101, Little River Beach State Park to Spruce Acres 

MMI VIII + 

Closed for 3 days 

There will be moderate structure damage to the bridge at Big Lagoon, which will be 

closed for 2 days for temporary repairs. A bluff failure north of Patricks Point State Park 

will undermine the highway, closing the south bound lanes. The north bound lanes will 

be closed by a slide at Big Lagoon. 

41 Route 101 from Spruce Acres to Stone Lagoon 
MMI IX 

High liquefaction potential 

Restricted for 3 days 

There will be no structure damage here, but the road surface will be disrupted by lateral 

spreads produced by extensive liquefaction. Repairs such as fill and patch work will be 

necessary. Emergency traffic will be permitted to pass. 

42 Route 101, Freshwater Lagoon 

MMI VII 

High liquefaction potential 

Closed for 2 days 

Lateral spreading can be repaired within 2 days. Alternate route available. Possible 

tsunami flooding. 

43 Route 101, north of Freshwater Lagoon 
MMI IX 

High liquefaction potential 

Closed for 3 days 

There will be moderate structure damage with significant liquefaction effects. 

Emergency traffic permitted within 2 days. 

44 Route 101 (old segment), north of Freshwater Lagoon to Resighini Rancheria 

MMI VIII + 
Open 



76 



NORTH COAST SCENARIO 

There will be minor structure and roadway damage. The new segment to the east has 
large cut and fills in soft ground and could have ground displacements. 

45 Route 101, Resighini Rancheria to Klamath River 
MMI IX 

High liquefaction potential 

Restricted for 3 days 

There will be liquefaction damage to the roadway, but no bridges will be affected. The 

route will remain open to emergency traffic, with all traffic being permitted within 1 2 

hours. 

46 Route 101, Klamath River Bridge. Klamath 
MMI IX 

High liquefaction potential 

Closed for 3 days 

There will be major damage to the bridge across the Klamath River. Liquefaction will 

lead to damage to the bridge foundation and to the surrounding roadway. Possible 

tsunami flooding. 

47 Route 169, to Klamath Glen 

MMI VII to IX 

High liquefaction potential 

Closed for 1.5 days 

There will be moderate structure damage with repairs requiring temporary shoring and 

earthwork. There will be moderate damage to the road surface due to liquefaction. 

48 Route 101, Klamath River to False Klamath Cove 
MMI IX 

Moderate to high liquefaction potential 

Closed for 2 days 

There will be major damage to the Panther Creek Bridge with liquefaction damage to the 

roadway. Repairs will include temporary shoring and earthwork. Possible tsunami 

flooding. 

49 Route 101, False Klamath Cove to southern Crescent City 

MMI VII 
Restricted for 1 day 



77 



NORTH COAST SCENARIO 

There will be no significant structure or roadway damage, but according to Carver 
(1993), parts of this stretch have many landslides that are too small to map at this 
scale. 

50 Route 101, southern Crescent City 

MMI VIII + 

Potential tsunami inundation area 

Moderate potential for liquefaction 

Closed for 3 days 

This part of the road is between 1 and 30 feet (3 to 9 m) above sea level and will be in 

the tsunami inundation area. Structures will be damaged and blocked by debris. 

51 Route 101, northern Crescent City to Route 101/199 Interchange 

MMI VIII + 

Restricted for 2 days 

There will be only minor structure damage here with emergency traffic able to use city 

streets as alternate routes. 

52 Route 101. 101/199 Interchange 
MMI VIII + 

Moderate potential for liquefaction 

Closed for 1.5 days 

There will be only minor structure damage here with emergency traffic able to use city 

streets as alternate routes. 

53 Route 199 from Route 101 to Hiouchi 
MMI IX 

Moderate potential for liquefaction 

Closed for 2 days 

There will be moderate structure and roadway damage. 

54 Route 199, Hiouchi to Cedar Springs 
MMI VII 

High rockfall potential 

Existing landslides 

Closed for 2 days 

The steep east facing slopes above this road have moderate fracture densities and the 



78 



NORTH COAST SCENARIO 

existing slides contain serpentinite and serpentinite breccia. Numerous local rockfalls 
and small slumps will close the route. 

55 Route 199, Cedar Springs to Washington Flat 

MMI VII 

High potential for rock falls 
Closed for over 3 days 

This is one of only two roads leading into the study area from the north. The route has 
very steep slopes with numerous perched rocks above the roadway (Photo H-4). 
Rockfalls will block the roadway and the river in the narrow canyons, with the reservoir 
depth being a few tens of feet. Carver (1993) indicates that some of the abandoned 
river terraces above the active channel along the upper Smith River are fluvial or lake 
sediments deposited upstream of large landslide dams. 








\ - 
Photo H-4 Route 199 between Cedar Springs and Washington Flat. 

56 Route 199, Washington Flats to Oregon 

MMI VII 
Open 

The tunnel 3 miles (5 km) south of the Oregon border is well over 1,800 feet (550 m) 
long. It will likely suffer some minor cracking and settlement problems, but it will be 
open with only minor traffic delays. 



79 



NORTH COAST SCENARIO 

57 Route 101, Kings Valley 

MMI VIII + 
Open 

58 Route 101, Smith River Bridge 
MMI IX 

High liquefaction potential 

Closed for 3 days 

The area near this bridge is highly susceptible to liquefaction (Carver, 1993). There will 

be major damage to the bridge across the Smith River and liquefaction will damage the 

surrounding roadway. 

59 Route 197 along the Smith River 
MMI IX 

Moderate to high liquefaction potential 

Closed for 1 day 

Only the lower reaches of this valley have high liquefaction potential. Because there are 

no structures along this route, the only possible damage will be pavement disruption 

from liquefaction. 

60 Route 101, Fort Dick to Smith River 
MMI IX 

Moderate to high liquefaction potential 

Closed for 2.5 days 

There will be moderate structure damage here. Liquefaction will damage the roadway 

and structures. 

61 Route 101, Smith River to Smith River Rancheria 

MMI IX 

Moderate to low potential for liquefaction 

Open 

62 Route 101. Smith River Rancheria to the Oregon Border 

MMI VIII + 

Open 

There will be only minor structure cracking and movement along this route. 



80 



NORTH COAST SCENARIO 

AIRPORTS 

General Characteristics 

Major and secondary airports in the planning area are shown on Map AR. The sites and facilities 
of the two major commercial airports served by regularly scheduled flights and the two largest 
secondary airports are listed in Table A-1 . The Arcata-Eureka and McNamara airports were 
visited, surveyed, and reviewed for potential earthquake damage. Roads to and from the airports 
were also assessed for potential impairment to access and egress routes subject to liquefaction, 
landslides, and damage to bridges and overpasses. Eleven secondary local airports were also 
visited. In this scenario where surface transport will be severely curtailed, and the area will be 
accessible mainly by air, airports will be a valuable resource to receive supplies and transport 
casualties. 

Only the Arcata-Eureka Airport and the McNamara Field in Crescent City are capable of handling 
C-130 aircraft, which require 5,000-foot runways for normal operations. Under special 
conditions, the C-130 type aircraft are capable of using unimproved runways or major roads. 

Other major commercial and military airports available for emergency relief outside the immediate 
planning area are: 

1 . McClellan Air Force Base in Sacramento, Sacramento County, California 

2. Travis Air Force Base in Fairfield, Solano County, California 

3. Beale Air Force Base in Marysville, Yuba County, California 

4. Medford-Jackson County Airport in Medford, Jackson County, Oregon 

These airports are accessible to U.S. Interstate Highway 5, and are less than an hour's flight time 
from the planning area. 

Seismic Considerations 

Earthquake concerns for airports fit the following three categories: 

1 . Ground access and egress 

2. Damage to runways and taxiways 

3. Damage to buildings, including control towers 

The minimum requirements for emergency operations are ground access and egress at the airport 
and usable runways and taxiways. Damage to or collapse of buildings, including the control tower, 
will not prevent emergency operations, particularly for military airlift operations. Ground access and 
egress implies that vehicles can come and go between the airport and the affected communities. 
Access problems can be created by collapse of adjacent freeway structures, road blockage by 

81 



NORTH COAST SCENARIO 

TABLE A-1 
COMMERCIAL AND MAJOR SECONDARY AIRPORTS 



AIRPORT 


CITY 


COUNTY 


RUNWAY LENGTH 


SITE 
LOCATION 

MM 
INTENSITY 


Arcata-Eureka 
McNamara 
Murray Field* 
Rohnerville 


McKinleyville 
Crescent City 
Eureka 
Rohnerville 


Humboldt 
Del Norte 
Humboldt 
Humboldt 


6,000 and 4,500 feet 
2 at 5,000 feet 
3,000 and 2,000 feet 
4,000 feet 


VIII + 

VIII + -IX 

IX 

VIII + 



* High liquefaction potential 

nearby landslides, and settlement due to liquefaction. Access considerations also must include the 
operation of utilities such as power, telephone, and water. On-site aircraft fuel storage is another 
important consideration, especially if supplies have to be brought in from long distances. 

Runway damage can render an airport unusable for emergency flights. The most serious threat to 
runways is damage from liquefaction of the underlying soils. Liquefaction can result in breaks in the 
pavement with differential settlements and lateral spreading of adjacent parts of runways. Federal 
Aviation Administration (FAA) regulations require the closing of a runway when there is a break (i.e., 
crack) in the pavement 3 or more inches wide. Damage to pavements from liquefaction can easily 
cause this much separation. 

The 1964 Great Alaska earthquake (M9.2), provided an excellent test of airport operations during an 
emergency. Of 64 airports inspected after the earthquake, 13 had runway or taxiway damage. 
Nevertheless, virtually all were operational within hours after the event. Some resourcefulness, 
however, was required. For example, the collapse of the control tower at Anchorage International 
Airport required use of radios in a grounded plane for air traffic control. 

During the 1 989 Loma Prieta earthquake (M7), Oakland International Airport lost 3,000 feet of 
runway. Runway damage also closed Alameda Naval Air Station for over 2 months. San Francisco 
International Airport was closed for 13 hours. Its control tower suffered minor damage, a cargo 
building suffered major damage, and some passenger terminals experienced extensive nonstructural 
damage, including water damage from fire sprinkler heads impacted by swinging suspended ceilings 
(EERI, 1990). 



82 



NORTH COAST SCENARIO 

Planning Considerations 

As it did in the 1 964 floods, air transport will play an important role in the earthquake and tsunami 
response operations because closure of the overland routes will isolate the area. Because the major 
population centers in the central planning area are in Eureka and Crescent City, the use of the 
Arcata-Eureka and McNamara airports will be crucial. The Crescent City Airport and the Arcata- 
Eureka Airport can take C-130 aircraft. 

The use of helicopters to transport people and material for search and rescue, general damage 
assessment, and the movement of critical supplies and light equipment should be given a high 
priority in planning. The U.S. Coast Guard Station at the Arcata-Eureka Airport has helicopters and 
associated facilities. Unfortunately, as presently constituted, the Coast Guard Station on the Samoa 
Peninsula will be destroyed by the tsunami. 

Planning Scenario 

Emergency air transport to and from the disaster area is vital to response activities, particularly 
during the first 72 hours. The best options under these scenario conditions will be Arcata-Eureka 
Airport and McNamara Field in Crescent City. Most small outlying airports in the planning area will 
be useable for small fixed wing aircraft and helicopters. They could be used to evacuate casualties 
and bring in key personnel and supplies. However, the condition of each would have to be 
determined, as some may be damaged or inaccessible due to road damage. Local emergency 
officials should consider these problems by referring to the damage assessments listed below. 

Damage Assessments 

Damage assessments have been postulated for certain facilities as set forth below. The statements 
regarding the performance of facilities are hypothetical and intended for planning purposes only. 
They are not to be construed as site-specific engineering evaluations. Outage and repair times 
assume that materials, equipment, and human resources are available concurrently for each damage 
locality. They will probably not be available concurrently, and outages could be much longer than 
estimated here. The locations of airports are shown on Map AR. 

MAP NO . AIRPORT FACILITIES 

A1 Shelter Cove (landing strip) 

MMI VIII + 

Open 



83 



NORTH COAST SCENARIO 



3,400 feet long, 75 feet wide 

Single wheel 30,000 pounds 

None 

None 

5 single or multiple engine 
Reactivation of existing landslide to east and landslides in surrounding areas of landslide 
potential will damage local roads impeding access to airport. 



Runway: 
Wheel Weight: 
Fueling Facility 
Repair Facility: 
Based Aircraft: 



A2 



Garberville 
MMI VIII + 
Open 
Runway: 
Wheel Weight: 
Fueling Facility: 
Repair Facility: 
Based Aircraft: 



3,050 feet long, 75 feet wide 

Single wheel 30,000 pounds 

Yes 

None 

16 single engine 

Airport is built on a thin fluvial terrace deposited on beveled sedimentary bedrock 
just east of the Eel River. The airport is only large enough for single and dual engine 
small aircraft and helicopters. Highway 101 will be closed for 3 days south of Benbow 
and north of Phillipsville due to landslides. Therefore, the airport will serve the local area 
only. 



A3 



Dinsmores 
MMI VIII + 
Open 
Runway: 
Wheel Weight- 
Fueling Facility: 
Repair Facility: 
Based Aircraft: 



2,510 feet long, 48 feet wide 



None 

None 

1 single engine 

Highway 36 will be closed to the east and west for 2 days, impeding access to the 
airport. 



A4 



Rohnerville 

MMI VIII + 

Open 

Runway: 



4,005 feet long, 100 feet wide 



84 



NORTH COAST SCENARIO 

Wheel Weight: Single wheel 30,000 pounds 

Fueling Facility: Yes 

Repair Facility: Yes 

Based Aircraft: 35 single and multi-engine aircraft and 1 helicopter 

Local roads will be open with access to portions of Highway 101. 



A5 



Kneeland 
MMI VII 
Open 
Runway: 
Wheel Weight: 
Fueling Facility: 
Repair Facility: 
Based Aircraft: 



2,270 feet long, 60 feet wide 

Single wheel 13,000 pounds 

None 

None 

1 helicopter 

Airport is remote from urban area but serves local residents. Local roads will be closed 
by reactivation of existing landslides and Highways 299 and 36 will be closed where 
local roads intersect highways. 



A6 



Eureka Municipal, Samoa Peninsula (landing strip) 

MMI IX 

Tsunami inundation zone 

High liquefaction potential 

Closed for an extended period 

Runway 2,700 feet long, 75 feet wide 

Wheel Weight: Single wheel 10,000 pounds 

None 

Yes 

5 single engine aircraft 



Fueling Facility: 
Repair Facility: 
Based Aircraft: 



Airport will be heavily damaged by liquefaction and tsunami inundation. 



A7 



Murray Field, Eureka 

MMI IX 

High liquefaction potential 

Closed for over 3 days 

Runways: 3,000 and 2,028 feet long, 75 and 50 feet wide 

Wheel Weight: Single wheel 19,000 and 5,000 pounds 



85 



NORTH COAST SCENARIO 

Fueling Facility: Yes 

Repair Facility: Yes 

Based Aircraft: 101 single and multi-engine aircraft 

Highways and local roads will be closed by lateral spreading due to liquefaction. 



A8 



Arcata-Eureka, McKinleyville 

MMI VIII + 

Open 

Runways: 

Wheel Weight: 



Fueling Facility: 
Repair Facility: 
Based Aircraft: 



5,998 and 4,500 feet long, 2 at 150 feet wide 

Single wheel 60,000 pounds, dual wheel 1 55,000 pounds, dual 

tandem 280,000 pounds 

Yes 

None 

1 1 single and multi-engine aircraft, 3 helicopters, 

2 military aircraft 
This airport has runways sufficient for C-130 aircraft. There will be some damage to 
buildings and structures which will hinder, but not prevent, airport use for emergency 
purposes. The control tower will have nonstructural damage and will need to be 
inspected before resuming full operation. The local stretch of Highway 101 and local 
roads will be open, but Highway 101 to the south and north will be closed for 3 days. 



A9 



Willow Creek 

This airport has been closed. Gravel mining has destroyed runway. 



A10 Hoopa Valley (landing strip) 

MMI VIII + 
Open 
Runway: 
Wheel Weight: 
Fueling Facility: 
Repair Facility: 
Based Aircraft: 



2,325 feet long, 50 feet wide 

Single wheel 10,000 pounds 

None 

None 

None 

This field is limited to small planes and helicopters. The airport will be damaged but 
usable. Routes 299 and 96 will be closed so access will be limited to the local area 
only. 



86 



NORTH COAST SCENARIO 



A1 1 Klamath Glen 

MMI IX 

High liquefaction potential 
Closed for over 3 days 



Runway: 
Wheel Weight: 
Fueling Facility: 
Repair Facility: 
Based Aircraft: 



2,400 feet long, 50 feet wide 

Single wheel 1 2,000 pounds 

None 

None 

None 



Runway will be damaged by liquefaction. 



A12 McNamara Field, Crescent City 

MMI VIM + 

Moderate to low liquefaction potential 

Open 



2 at 5,002 feet long, 1 50 feet wide 

Single wheel 30,000 pounds, dual wheel 43,000 pounds , dual 

tandem 100,000 pounds 

Yes 

Yes 

31 single and multi-engine aircraft 
Some airport structures will be damaged. The tsunami will close roads in southern 
Crescent City for 3 days, but there will be access to a restricted part of Highway 101 
north of the city. Local roads can be used to get around the closed 101/199 
interchange. 



Runways: 
Wheel Weight: 

Fueling Facility: 
Repair Facility: 
Based Aircraft: 



A13 Gasquet (Ward landing strip) 

MMI VII 
Open 
Runway: 
Wheel Weight: 
Fueling Facility: 
Repair Facility: 
Based Aircraft: 



2,990 feet long, 50 feet wide 

Single wheel 12,000 pounds 

None 

None 

None 



Route 1 99 will be closed to the east and west. 



87 



NORTH COAST SCENARIO 

A14 Smith River (Ship Ashore landing strip) 

MMI IX 

High liquefaction potential 
Closed for over 3 days 

Runway: Approximately 2,400 feet long, width unknown 

Wheel Weight: Unknown 
Fueling Facility: Unknown 
Repair Facility: Unknown 
Based Aircraft: Unknown 

Landing strip shown on USGS topographic maps, but not listed by FAA. Engineers at 
the Del Norte County Community Development Department are not aware of a facility 
there. Probably abandoned with unserviceable runways and no facilities. Liquefaction 
will damage runways. Route 101 open to north into Oregon and south to Route 
101/197 interchange. 



88 



NORTH COAST SCENARIO 

MARINE FACILITIES 
General Characteristics 

The two major marine facilities along the coastline of the planning area are at Eureka and Crescent 
City, and their locations shown on Maps SHM-1 and SHM-2. In addition, there are other small 
harbors such as Trinidad, for yacht clubs and pleasure craft. Vessels using the harbors are mainly 
commercial and private ships. Although Humboldt Bay has provided ship mooring for lumber and log 
exporting for many years, the volume of lumber and logs has recently declined. Since the days 
when redwood logging was of prime interest in Crescent City, and the Citizens Dock project in 
Crescent Harbor was built in 1 950 "through community group efforts to save the lumber and fishing 
industries" (Conlin, 1991), the volume of its commercial shipping industry has diminished. 

Except for the U.S. Coast Guard Reservation stations, no major military marine facilities are in the 
planning area in comparison to those found in other parts of California such as Hunter's Point Naval 
Shipyard in San Francisco or the U.S. Pacific Naval Base in San Diego. 

The Humboldt Bay harbor is a natural harbor with the Samoa Peninsula protecting it from the ocean. 
The North and South jetties were constructed to reduce the hazard of entering the harbor. The 
jetties were originally constructed with large rocks hauled in by railroad. In recent years the two 
jetties have been rehabilitated by using concrete dolos to provide increased stability against heavy 
wave action. 

Seismic Considerations 

Information collected on the seismic performance of docks, jetties, warehouses, equipment, and 
support structures in previous earthquakes was extrapolated for this scenario. 

Seismic events of particular interest to this section are: 

a) The 1960 South Chile earthquake (M9.5) and the 1964 Great Alaska earthquake (M9.2), 
both of which generated tsunamis that hit Crescent City 

b) The 1954 Eureka earthquake (M6.5) 

In the 1 954 Eureka earthquake, "The Hammond Lumber Company at Samoa had some of its 
structures on a hydraulic fill along the waterfront. The fill was said to have been placed about 
1940. A large one story wood frame warehouse at this location settled vertically and lurched 
slightly toward the bay. Other wood frame buildings had some indications of damage, possibly due 
in part to settlement" (Steinbrugge and Moran, 1957). 

89 



NORTH COAST SCENARIO 

The 1 960 South Chile earthquake "triggered a small wave that travelled north in the Pacific for 1 5 
hours. The surge reached 12 feet and lasted for 23 minutes, dumping water and debris on Crescent 
City streets. ...In that instance, two vessels were lost in the harbor, and about $30,000 in damage 
was reported" (Conlin, 1991). 

The biggest seismic impact on Crescent City, however, occurred after the 1 964 Great Alaska 
earthquake generated a tsunami that spread southward in the Pacific Ocean. Accounts of the 
impact of this event on Crescent City are summarized earlier in the report. 

Other accounts of the vulnerability of harbors to unstable soils, liquefaction, and tsunamis are 

documented in reconnaissance reports on past seismic events in Alaska after the 1 964 earthquake 

and the San Francisco Bay area after the 1 989 Loma Prieta earthquake: 

"At Seward, Alaska, the 1 964 earthquake was intense and of long duration. Docks 
apparently began sliding under the water surface soon after the earthquake began and 
continued during the shaking. One 200-ton wharf crane disappeared in the slide and 
was never found again. Another jumped its rails. The ground surface under 
Resurrection Bay at Seward drops off rapidly from the shoreline, being about 200 feet 
deep at about 900 feet from the shore. This steep gradient on unstable soils readily 
explains the landslide with its destruction of docks and the "lost" crane. 

Submarine landslides also destroyed the port facilities at Valdez and Whittier, Alaska, in 
the 1 964 shock. Substantially lesser damage was sustained to the docks at Anchorage, 
Alaska, although a crane overturned at one of them. Damage also occurred at many 
other locations along the southern Alaska coastline. 

The damage to port facilities was compounded by the spectacular tsunami and its 
effects. ...Valdez also had tsunami damage due to submarine landsliding. The ship 
Chena was moored at the dock which collapsed. Lives were lost on the dock and the 
ship. ...The highest wave rose to 23 feet. Valdez has since been rebuilt on a different 
site with the view of minimizing the hazard from future submarine landslides and 
tsunamis" (Steinbrugge, 1982). 

In the 1989 Loma Prieta earthquake (M7.0) at the Port of San Francisco and the Port of Oakland: 

"The primary cause of damage (at the Port of San Francisco) was liquefaction of the fill 
material, which resulted in the settlement of the piers supported by fill relative to the 
portions of the piers supported by piles. Settlement continued for several weeks after 
the earthquake. ...Because of significant structural damage at different locations along 
the waterfront, some buildings were condemned. Structural damage included cracked 
concrete walls and displaces asphalt decks in warehouses on Piers 45 and 48, caused 
by settlement of underlying fill; cracking and collapse of unreinforced clay tile walls in an 
office building on Pier 70; and the buckling of columns at the clock tower in the Ferry 
Building. ...Other damage at the port included many broken water mains, many broken 
batter piles, cracked decks above the piers, and damage to five container cranes. 

"As with the Port of San Francisco, the primary cause of damage (at the Port of 
Oakland) was liquefaction of fill and the resulting settlement and spreading of areas of 
fill relative to areas supported by piles. The many broken water and fire lines washed 
the fine materials from the soil, causing both settlement and uplift of the asphalt 

90 



NORTH COAST SCENARIO 



pavement at numerous locations throughout the port. ...Wood piles with concrete 
followers were broken at Middle Harbor, resulting in condemnation of a building that 
was supported on these piles. The piles broke at the wood-concrete interface. 
Throughout the port, damage to piles and the settlement of fill occurred up to three 
weeks after the earthquake. ...At the Seventh Street terminals the crane rails that were 
on fill settled as much as 12-15 inches relative to the rail on piles, rendering the cranes 
inoperable. The rail spur serving Terminal 40 is... out of service because of horizontal 
and vertical displacement of the rails of fill relative to a portion of the spur supported by 
piles. Significant settlement and separation of the truck access road to Terminals 35-38 
at the Seventh Street Complex occurred as a result of liquefaction. ...The Seventh 
Street Complex was finally shut down" (EERI, 1990). 



As can be seen from accounts of past earthquakes, similar damage patterns appear in marine 
facilities due to ground settlement, liquefaction of soils due to strong shaking, and damage of port 
facilities and equipment due to tsunamis. Harbors along the coast of Humboldt and Del Norte 
counties have the same seismic considerations in terms of their vulnerability to earthquakes, and 
accordingly, should be expected to experience similar damage patterns. 

Planning Considerations 

Most of the docks in Eureka are supported on piles. While they are not expected to suffer severe 
damage from shaking, damage will result from tsunami effects. Moreover, tarmacs, aprons, access 
roads, and other paved surfaces over fill areas will fail due to settlement and liquefaction. 

Pipelines, water utilities, storage tanks, and other facilities important to terminals and docks are 
susceptible to rupture where they cross areas of soft soil near the docks. Restricted egress and 
access to terminals and docks from liquefaction-damaged streets will be more common than 
liquefaction damage to pile supported docks. Finally, it is the tsunami that will severely impair the 
marine facilities. To facilitate access and to create fire breaks, earth moving equipment should be 
available for use after the tsunami. Fire was a major problem in the 1 993 Japanese earthquake 
(EERI, 1993). Firefighters were unable to reach the fire due to the debris left by the tsunami. 

Planning Scenario 

We expect impacts due to the tsunami in Crescent City that are at least comparable to those that 
occurred in 1 964. While the city prudently has restricted land use adjacent to the harbor area, new 
development south of town along the shoreline is vulnerable. Damage to docks and other structures 
will equal or exceed that experienced in 1 964. 



91 



NORTH COAST SCENARIO 

The Humboldt-Arcata Bay is partially protected from tsunami damage by the Samoa Peninsula and 
South Spit. We expect the peninsula to be overtopped, and all structures and lifelines to be severely 
damaged. Without sufficient warning time and evacuation, casualties could be heavy on the Samoa 
Peninsula, as was the case with a tsunami that struck an island west of Nicaragua in 1992. The 
earthquake and tsunami damage will release any hazardous materials used in the pulp mills on 
Samoa Peninsula, adding to the response problems. 

The Samoa Peninsula will take the brunt of the tsunami damage in Humboldt Bay, allowing only 
minor waves to reach Eureka. No such barriers exist in Crescent City, leading to broad tsunami 
inundation and damage in the downtown area (Maps S-1 and S-2). We expect more severe 
liquefaction damage in the Humboldt-Arcata Bay area and more severe tsunami damage in Crescent 
City. 

Usable docks in the heavily damaged areas will require emergency power and special off-loading 
capabilities. Truck traffic to and from the ports may have to be rerouted via undamaged access 
routes. Appropriate coordination efforts with other ground transport services will be required for 
efficient transfers. We expect marine transport will play minor roles in emergency response efforts. 
Air transport should be coordinated with ground transport to select the most effective means of 
providing needed equipment and supplies to the stricken area. 

Serious disruption will last for a week, but problems could continue for up to a year. Typical 
problems include loss of electric power, damaged surface roads, debris from the tsunami, and 
damage to cranes and related facilities. 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Locations of marine facilities are shown on Maps SHM-1 and SHM-2. 

MAP NO. MARINE FACILITIES 
Ml Humboldt Bay Harbor 

MMI IX 

High potential for liquefaction 

Tsunami run-up zone 

92 



NORTH COAST SCENARIO 

Closed for 7 days 

Severe damage will result from strong ground shaking, liquefaction, and the tsunami. 

M2 Crescent City Harbor 
MMI IX 

Tsunami run-up zone 
Closed for an extended period 

Crescent City's harbor directly faces the ocean, and the tsunami damage will be even greater 
than that experienced in 1 964. Figure S-3 in the Geology and Seismology chapter compares 
the extent of inundation in the present scenario to that from the 1964 Alaska earthquake. 
The tsunami will heavily damage the pier areas and nearby structures, and will extend several 
blocks into the downtown area. 



93 



NORTH COAST SCENARIO 

RAILROADS 
General Characteristics 

With the changes that have occurred over the last two decades in the economics and development 
of the timber industry, the role of railroads in hauling freight has diminished considerably throughout 
the planning area. As a result, transport by railway is now limited to the North Coast Railroad 
(NCRR). Based in Eureka, the NCRR operates from near Areata on the north to the City of Willits in 
the south. It also provides occasional service to Fairhaven on the Samoa Peninsula. Selected 
locations, bridges, and railway facilities were surveyed in the field for potential earthquake damage. 

The major active north-south railroad line in northwestern California closest to Humboldt and Del 
Norte counties is operated by the Southern Pacific Transportation Company (SPTCO) and is outside 
the planning area, 100 miles (160 km) due east of Eureka and Crescent City. This railway line runs 
parallel to Interstate 5 which stretches from San Diego near the Mexican Border, through Oregon, 
and north to Washington. Any emergency materials and equipment transported over this SPTCO 
line would have to be flown in from McClellan Air Force Base in Sacramento, Travis Air Force Base 
in Fairfield, Beale Air Force Base in Marysville, or Medford-Jackson County Airport in Oregon, to 
airports in Eureka and Crescent City, because highways into Humboldt and Del Norte counties from 
the Sacramento Valley and from Oregon will generally be impassable (refer to Highways Map H-3). 

As shown on Map AR, there are three local railroad lines: 

1 . The apparently unused line from Areata to the Samoa Peninsula. 

2. The line that runs from Areata, through Eureka, down to Fortuna, to Rio Dell and Scotia in 
the south, along the Eel River portion outside the planning area to Dos Rios and reaches its 
terminal at Willits. 

3. The seldom used line that runs from the northern part of Areata to the Mad River near the 
community of Korbel. 

Over the years, segments of the North Coast Railroad line have not been maintained and are not in 
current use. Currently, there are no extensive railway lines in Del Norte County. 

For planning purposes within the study area, Railroad access to the outside for post-earthquake 
emergency freight haulage (including heavy equipment and critical supplies) will be unavailable 
throughout the 3 day scenario. The route will be blocked by landslides and lateral spreading, and 
may not be totally functioning for a month or longer. 



94 



NORTH COAST SCENARIO 



Seismic Considerations 

The coastal railroad lines in the Eureka/Arcata marine terminal areas in Humboldt and Areata bays, 
run along bay margins which are subject to liquefaction and tsunami effects. Rail lines located on 
such "poor ground" in low-lying areas are highly susceptible to severe damage. For an excellent 
source of information on damage patterns to be expected during a major earthquake, refer to the 
paper on the effects of the 1964 earthquake on the Alaska Railroad (McCulloch and Bonilla, 1970). 

Railway bridges do not necessarily experience major damage except in areas subject to ground 
failure. However, when severe bridge damage does occur, it may involve a lengthy period for major 
repairs, which may last up to 14 days. The North Coast Railroad system has a roadbed line that 
crosses over the Little Salmon fault, bridges various sloughs, creeks and rivers including the Eel 
River, and runs along bay margins susceptible to liquefaction and tsunami run-up. 

The 1 964 Great Alaska earthquake produced tsunamis that severely damaged several coastal 

communities. One of the hardest hit was the City of Seward where railroad lines in waterfront dock 

areas were damaged: 

"A large swell broke over the Alaska Railroad dock area, lifting the flat cars off the 
tracks. ...An 80-car freight train on the tracks between the Standard and Texaco tanks 
was just ready to start moving north. Its last 40 cars were filled oil tankers and as the 
fire swept onto shore, the tankers caught fire in a chain reaction of exploding cars down 
the track toward the Texaco yard. ...The first seismic sea wave is reported to have 
spanned the width of the bay as it entered the Seward area and to have been 30 to 40 
feet high as it neared the head of the bay. Burning oil covered much of its surface. 
Carrying boats, houses, and railroad cars collected from the Seward waterfront area, the 
wave crashed over the railroad embankment. .."(Steinbrugge, 1982). 

A brief written assessment of the impact of the 1992 Cape Mendocino earthquake (M7) on the 

North Coast Railroad indicates that little damage occurred on its lines to the City of Willits (EERI, 

1992a): 

"The North Coast Railroad operated between Willits and Eureka transporting gravel and 
lumber. The two trains operating on the day of the first earthquake were stopped in 
accordance with company policy. Trains were cleared to proceed to their terminals after 
the tracks, tunnels, and bridges were inspected. On the next day, Sunday, a normal 
non-operating day, a more detailed inspection was made. The tracks were cleared of 
minor loose landslide material and were re-ballasted at one minor settlement. There was 
no settlement at bridge abutments. Train service returned to normal on Monday without 
loss of service." 

During the 1994 Northridge earthquake (M6.7) in the greater Los Angeles region, "A 64 car freight 
train traveling through Northridge derailed at the time of the earthquake. There were 1 5 tank cars 
carrying sulfuric acid, and 8,000 gallons of acid spilled from one of the cars. Also, 2,000 gallons of 



95 



NORTH COAST SCENARIO 

diesel fuel spilled from the locomotive. Train service was restored by 2:00 a.m., January 19th, and 
the area was cleared of debris by January 21st (four days after the earthquake)" (EERI, 1994). 

Railroad facilities and tracks are also subject to closure by major damage to freeway overpasses, 
bridges built over slough areas, and other traffic interchanges constructed over rail lines. As 
indicated by damage to the Struve Slough bridges during the 1 989 Loma Prieta earthquake (EERI, 
1 990) and collapse of the Interstate 5/State Road 1 4 interchange during the 1 994 Northridge 
earthquake (EERI, 1 994), existing interchanges, overpasses, and bridges are vulnerable to significant 
damage and collapse. The Fields Landing overpass of Highway 101 which collapsed onto the North 
Coast Railroad line during the 1 980 Gorda Basin earthquake (M7) is yet another example. 

Planning Considerations 

Privately owned railroads, because of their repair capabilities, including extensive use of outside 
contractors, are generally able to solve most of their reconstruction problems with little attention 
from governmental emergency response organizations. However, because the NCRR is a public 
agency, it may need to obtain outside resources through Humboldt County's Office of Emergency 
Services, and will most likely be eligible for state and federal disaster assistance. 

Complete restoration of rail service throughout the area could take several weeks to many months. 
The relationships between the railroad, other systems of transport, and utility lifelines should be 
reviewed to identify likely response and service restoration problems and to set repair priorities 
before the scenario earthquake occurs. 

Planning Scenario 

The rail lines along the Eel River, Humboldt Bay, and Areata Bay, will be displaced by liquefaction 
and landslides and closed for repairs for several weeks. All movable span bridges in MMI VIII + to 
IX zones are subject to misalignment due to heavy ground shaking. Many of the older bridges will 
be closed along the NCRRs right of way. 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 



96 



NORTH COAST SCENARIO 

each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. The locations of the NCRR are shown on Map AR. 

MAP NO. RAILROAD LOCATIONS 

R1 North Coast Railroad, from the Mendocino County line to South Fork 

MMI VII to IX 
Potential for landslides 
High potential for liquefaction 
Closed for more than 7 days 

Embankments will be damaged. The bridge over the Eel River at Dyerville will be 
misaligned and will be closed to traffic from 2 to 8 days. There will be numerous clo- 
sures due to landslides which will block or misalign tracks and bridges. 

R2 North Coast Railroad, Dyerville loop 

MMI VIII + to IX 
Potential for landslides 
High potential for liquefaction 
Closed for more than 7 days 

Large slide with high relief on ridge above railroad indicates slide mass will close 
railroad above the Eel River. 

R3 North Coast Railroad, bridge at Scotia, South Fork Eel River 

MMI VIII + to IX 

Potential for landslides 

High potential for liquefaction 

Closed for more than 7 days 

Liquefaction and landslides will block or misalign the tracks, and the bridge across the 

South Fork Eel River (Photo R-1). 

R4 North Coast Railroad, beneath Fields Landing Overpass 

MMI IX 

High potential for liquefaction 
Closed for more than 7 days 

The overpass on Route 101 could fall onto the tracks as occurred in 1980. Beneath 
the overpass the railroad tracks cross a drainage area underlain by fine sand which is 
subject to liquefaction (Photo R-2). Either or both situations will stop service on this 
segment. 



97 



NORTH COAST SCENARIO 




Photo R-1 Railroad bridge across South Fork Eel River at Scotia. 




Photo R-2 Railroad tracks beneath Fields Landing overpass. 



98 



NORTH COAST SCENARIO 

R5 North Coast Railroad, north of Fields Landing to Eureka and Areata 

MMI VIII + to IX 

High potential for liquefaction 

Closed for more than 7 days 

Line follows Humboldt Bay eastern shoreline, which is subject to liquefaction. 

R6 North Coast Railroad, Samoa to Areata (non-operational) 

MMI IX 

High potential for liquefaction 
Tsunami run-up zone 
Closed for an extended period 

R7 North Coast Railroad, Areata to Blue Lake 

MMI VII to IX 

High potential for liquefaction 
This seldom used segment will be closed for more than 7 days 



99 



UTILITY LIFELINES 



SCENARIO MAPS AND DAMAGE ASSESSMENTS 

ARE INTENDED FOR EMERGENCY PLANNING 

PURPOSES ONLY 



THEY ARE BASED ON THE FOLLOWING HYPOTHETICAL 
CHAIN OF EVENTS: 

1 . A PARTICULAR EARTHQUAKE OCCURS 

2. VARIOUS LOCALITIES IN THE PLANNING AREA 
EXPERIENCE A SPECIFIC TYPE OF SHAKING OR 
GROUND FAILURE 

3. CERTAIN CRITICAL FACILITIES UNDERGO DAMAGE AND 
OTHERS DO NOT 

THE CONCLUSIONS REGARDING THE PERFORMANCE OF 
FACILITIES ARE HYPOTHETICAL AND AND NOT TO BE 
CONSTRUED AS SITE-SPECIFIC ENGINEERING EVALUATIONS. 
FOR THE MOST PART, DAMAGE ASSESSMENTS ARE STRONGLY 
INFLUENCED BY THE SEISMIC INTENSITY DISTRIBUTION MAP 
DEVELOPED FOR THIS PARTICULAR SCENARIO EARTHQUAKE. 
THERE IS DISAGREEMENT AMONG INVESTIGATORS AS TO 
THE MOST REALISTIC MODEL FOR PREDICTING SEISMIC 
INTENSITY DISTRIBUTION. NONE HAVE BEEN FULLY TESTED 
AND EACH WOULD YIELD A DIFFERENT EARTHQUAKE 
PLANNING SCENARIO. FACILITIES THAT ARE PARTICULARLY 
SENSITIVE TO EMERGENCY RESPONSE WILL REQUIRE A 
DETAILED GEOTECHNICAL STUDY. 

THE DAMAGE ASSESSMENTS ARE BASED ON THIS SPECIFIC 
SCENARIO. AN EARTHQUAKE OF SIGNIFICANTLY DIFFERENT 
MAGNITUDE ON THIS OR ANY ONE OF MANY OTHER FAULTS 
IN THE PLANNING AREA WILL RESULT IN A MARKEDLY 
DIFFERENT PATTERN OF DAMAGE. 



NORTH COAST SCENARIO 

ELECTRIC POWER 
General Characteristics 

Electric power is supplied to Humboldt County by Pacific Gas & Electric (PG&E) and to Del Norte 
County by Pacific Power and Light Company. Routes of transmission lines and the location of a 
major generating facility and substations that serve the area are shown on Maps EGP-1 and EGP-2 
and AR. The major generating plant in the planning area and representative substations were 
reviewed for vulnerability to seismic effects. 

Sources of electric power in Humboldt County are the PG&E fossil fuel generating plant near Buhne 
Point, three transmission lines from outside the area, and private cogeneration plants in the area. 
The Humboldt Bay Power Plant is fueled by natural gas produced at the Tompkins Hill Gas Field and 
by gas transmitted to the plant by a PG&E-operated 12-inch pipeline from Red Bluff. 

Electrical power for the Crescent City area is managed by Pacific Power and Light Company. The 
supply lines come through Grants Pass substation in Oregon, with 90 percent of the power 
originating at the Jim Bridger Plant in Wyoming. The remaining 10 percent comes from two hydro- 
electric plants in Oregon at Klamath River and Tokedy. The power is distributed to the city starting 
from the Del Norte Substation, about 5 miles (8 km) north of town. 

Table E-1 is a listing of the principal communities served by PG&E in Humboldt County and Pacific 
Power and Light Company in Del Norte County. In addition to the two major electric power 
companies listed in Table E-1, privately owned power plants (Fairhaven Power Company, Simpson 
Company, and the Louisiana Pacific Company on the Samoa Peninsula, and Ultra Power Company 
near Blue Lake) generate electric power for sale to PG&E. 

Table E-2 lists the public and private electric power plants in the planning area. The PG&E power 
plant located on Humboldt Bay near Buhne Point is the sole public utility system that generates 
electric power within the planning area. 

Within a complete electric power service system there are many critical elements including four 
primary components: 

1 . Generating power plants 

2. High voltage transmission lines 

3. Transformer and switchyard substations 

4. Distribution lines 



101 



NORTH COAST SCENARIO 

TABLE E-1 
PRINCIPAL COMMUNITIES SERVED BY ELECTRIC POWER COMPANIES 



UTILITY COMPANY 


COUNTY 


COMMUNITY 


Pacific Gas & Electric 


Humboldt 


Eureka 

Areata 

McKinleyville 

Blue Lake 

Trinidad 

Fortuna 

Hydesville 

Loleta 

Rio Del 

Bridgeville 

Miranda 

Weott 

Orick 

Petrolia 

Ferndale 


Pacific Power and Light Co. 


Del Norte 


Crescent City 
Smith River 
Gasquet 
Klamath 
Fort Dick 



TABLE E-2 

ELECTRIC POWER GENERATING PLANTS 
IN THE PLANNING AREA 







SITE LOCATION 


ELECTRIC POWER PLANT 


LOCATION 


MM INTENSITY 


PG&E* 


Buhne Point 


IX 


Fairhaven Power Co.** 


Samoa Peninsula 


IX 


Louisiana Pacific Co.** 


Samoa Peninsula 


IX 


Simpson Co.** 


Samoa Peninsula 


IX 


Ultra Power Co.** 


Blue Lake 


VIII + 



* The major electric utility company in Humboldt County 
*" Small, privately owned plant 



102 



NORTH COAST SCENARIO 



Seismic Considerations 

Large earthquakes generally disrupt electric power service. Sources of disruption may come from 
one or more of the following three elements: 

1 . Disruption of the source of supply 

2. Damage to transmission facilities 

3. Damage to switching and transformer facilities 

4. Damage to the distribution system 

Sources of electric power include generating plants, such as fossil, hydro and nuclear power plants, 
and power supplied from transmission inter-ties with power grids with many diverse power sources. 
Generating facilities are typically rugged. For instance, the Moss Landing Plant (2,000 MW) on 
Monterey Bay was shaken at MMI VII by the Loma Prieta earthquake (M7) but damage to the seven 
generating units was relatively modest (EERI, 1990). 

Transmission facilities consist of high-voltage lines and substations. Generally, transmission towers 
and lines are resistant to damage from ground shaking, but they can be damaged by ground 
movements caused by surface fault rupture, liquefaction, or landslides. The effects of ground 
movements, however, are much more local than are ground shaking effects. Transmission facilities 
are vulnerable mainly at high-voltage substations (_>220 kV). During the Loma Prieta earthquake, 
three such substations (Moss Landing, Metcalf, and San Mateo) suffered major damage. Within the 
Moss Landing substation (MMI VII), about 18 miles (29 km) from the epicenter, four live-tank circuit 
breakers were severely damaged as well as 10 of 12 current transformers (EERI, 1990). The type 
of damage experienced at Moss Landing, and the other two substations, is not without precedent. 
In fact, high-voltage substations generally are considered the least seismically resistant element in 
electric power supply systems. 

At Seward, Alaska, the 1964 earthquake (M9.2) and tsunami caused great damage to the electric 

power system: 

"Some storage tanks at the Standard Oil tank farm broke open during the earthquake 
and the oil ignited. The nearby building, housing the standby generators, burned, and all 
the equipment was destroyed. The 69-kV transmission line across the freshwater 
lagoon was demolished. Power poles and spans of conductors were destroyed in the 
old townsite by slides, destruction of the dock, movement or destruction of buildings, 
and by waves. The only electric service available after the earthquake was from an 
emergency generator that provided a limited amount of power at the hospital" (NAS, 
1973). 

The Great Alaska earthquake also generated the tsunami that inundated Crescent City on March 27, 
1964: 



103 



NORTH COAST SCENARIO 



"...a number of fires broke out in the harbor-front area in the city and south of town as 
electric lines were short circuited and oil tanks ruptured. However, water over Highway 
101 prevented fire trucks from proceeding immediately to the burning tanks. ...There 
was a continuous crashing and crunching sound as the buildings gave way and 
splintered into rubble, and there were flashes from high powered electrical lines shorting 
out that resembled an electrical storm approaching from the east, except some of the 
flashes were blue" (Griffin, 1984). 



At the PG&E generating plant during the 1 992 Petrolia earthquake (M7) series: 

"The peaking unit operating at the time of the first event tripped off and could not be 
started again due to condenser tube leaks and low water levels in the steam drum. The 
other peaking unit was 'hot' and took 6 hours to reach operating output. It then tripped 
during the second event. Despite these events, there was adequate power supply 
because of the availability of the outside sources. Local outages were caused by 
transformer fires, wires welded together, wires slapping together, and wires burning 
down" (EERI, 1992a). 



The 1992 Landers earthquake (M7.5) in San Bernardino County provides excellent evidence of the 

performance of high-voltage transmission towers during a major earthquake: 

"Power service was disrupted for approximately 600,000 customers throughout the 
greater southern California region, including customers as far way from the epicenter as 
Santa Barbara and Los Angeles, owing to localized damage within the distribution 
system. The region is served by approximately eight electric utilities. Most of the 
service disruptions were for a few seconds or minutes, and service was restored to most 
other customers within 24 hrs. of the earthquake. There was no operational damage to 
the high-voltage systems and generating facilities. ...Power was retained in all of the 
230- and 500-kV transmission lines. Service was momentarily interrupted in a few 66- 
and 1 1 5-kV lines. Protective relays automatically trip circuit breakers open; however, 
the breakers close within a few seconds in case the electrical fault is merely transient. 
The electric utility in the epicentral area reported 29 of these momentary circuit 
interruptions in the high-voltage system. The surface rupture of the Landers event 
actually passed between the legs of a 230 kV steel truss transmission tower. The 
permanent horizontal ground displacement across the fault shifted one side of the tower 
base an estimated 8 ft (2.4 m) relative to the other side. As a result, the center of the 
tower twisted in torsion, buckling and breaking diagonal braces in the four legs. In spite 
of the distortion, the tower did not collapse and there was no disruption in service. The 
major source of power outage was distribution lines swinging together. Contact 
between distribution lines breaks the circuit either by burning out a nearby pole mounted 
fuse, which activates a circuit breaker, or by burning the conductor wire within the 
cable. Burning the conductor often causes the wire to separate and drop to the ground" 
(Lund, 1994). 



In the recent 1994 Northridge earthquake (M6.7), lattice transmission towers fared worse than 
ductile steel towers. The footing movement resulted in serious deformation of the towers and came 
very close to producing some tower failures. Caissons 10 feet in diameter and approximately 40 
feet in length were pulled 1 foot out of the ground. This scene will be duplicated in Humboldt 
County where lattice towers are in marshy areas. 



104 



NORTH COAST SCENARIO 

The Southern California Edison Company substation at Valencia where the equipment and towers 
were damaged heavily by the Northridge earthquake was visited by a member of the research team. 
The equipment at the substation had been anchored for lateral forces of 0.5 g. This substation, 
however, was in a valley where the water table is 5 feet below grade, so the tower problems 
resulted from strong shaking and probable liquefaction. 

Distribution systems operate at much lower voltages, have much greater redundancy, and are less 

vulnerable than transmission systems. There was relatively little damage to distribution systems 

after the Loma Prieta earthquake, with the damage described as being equivalent to that produced 

by a severe winter storm (EERI, 1990). The overall effect of the Loma Prieta earthquake on the 

electrical power system has been summarized as follows: 

"Approximately 1 .4 million consumers suffered interruption of their electrical service as 
a result of the earthquake. Within 48 hours, service had been restored to all but 26,000 
customers. Parts of Watsonville, however, were without electricity for 4 to 5 days" 
(McNutt, 1990). 

According to Savage and Matsuda (1994): 

"The problems caused by distribution system damage due to lines burning down, pole- 
mounted transformers burning out or falling, or trees and buildings pulling lines down 
[are] generally quick to repair, there may be enough instances of this damage in both 
towns and remote rural areas that individual customers or small groups of customers 
could be without service for several days. From a planning standpoint, electric power 
customers should plan on surviving without power or using their own emergency power 
for several days." 

The electric generating facilities listed in Table E-2, except that at Blue Lake, are within the tsunami 
run-up zone as shown on Maps EGP-1 and EGP-2. Tsunami damage will be extensive at the 
facilities on the Samoa Peninsula, but much less at Buhne Point where the run-up will extend only 
1/4 mile beyond the facility. 

Planning Considerations 

Sources of power to the planning area other than the power plants listed in Table E-2 come from 
outside and will be unaffected by the scenario earthquake and tsunami. Disruption of power service 
to institutions, businesses, and residences will come from damage to substations and local 
distribution systems. Customers especially sensitive to loss of electric power should maintain their 
own emergency sources (e.g., generators or batteries). 

Vital facilities and other lifelines discussed in the report, especially water supply, waste water 
treatment, and communications will be affected by interruptions in electrical power. Emergency 

105 



NORTH COAST SCENARIO 

planning for such facilities must recognize that power in certain areas can be out for extended 
periods. It is crucial that hospitals, emergency operations centers, water and waste water systems, 
and other vital facilities have their own emergency power sources. Those without emergency power 
sources must be identified, and appropriate procedures should be developed to compensate for this. 

Planning Scenario 

During the first 72 hours after the earthquake virtually all parts of the planning area will experience 
some loss of power, at least temporarily. The cities of Fortuna, Eureka, Areata, and Crescent City 
are in strongly shaken areas (MMI VIII + and IX) and will experience significant power outages. 
Service to most areas will be restored within 24 hours, but some parts of the cities and rural areas 
may experience outages lasting as long as 5 days. 

To continue high voltage service while repairs are being made, electric power will be distributed over 
alternate lines. The towers of high-voltage transmission lines crossing a large area of liquefaction 
along the marshlands of Humboldt/Arcata Bay will be damaged by settlement and subsidence. 

According to Savage (1993): 

"Lower voltage substation equipment and transmission lines are typically not affected by 
earthquakes. Even in the Northridge earthquake, with "direct hit" ground motions of 0.6 
to 0.9 + g, damage to 1 1 5 kV and lower voltages was limited. There will be, however, 
some electric system damage at low voltage due to lines slapping together and burning 
down, a few broken poles supporting distribution transformers, and downed lines caused 
by falling trees. Such damage is expected to be highly sporadic and is usually repaired 
quickly by local crews, so customers should not be out of service for more than a few 
hours or a day or so." 

Electric power supply is an absolute necessity in meeting today's societal needs. Unfortunately, 

electric power facilities are particularly vulnerable to major seismic events in areas of severe ground 

shaking (MMI VIII or IX), and/or deformation: 

"The time that it will take to restore full power under the best of conditions could be 
prolonged. While the resources may be available to rapidly deal with repairs to the 
system, the confusion and damage to such lifelines as communications and highways 
will create a substantial challenge. ...Emergency planning for power-dependent systems 
such as communication, water supply, fire fighting, and waste treatment should be 
cognizant of this likelihood" (Steinbrugge and others, 1987). 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 

106 



NORTH COAST SCENARIO 

repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Locations of electric power transmission lines and major power 
generation and substation facilities are shown on Maps EGP-1 and EGP-2 and AR. 

MAP NO. ELECTRIC POWER FACILITIES 
El Carlotta Substation 

MMI IX 

Out of service for 2 days 

E2 Fortuna Substation 

MMI IX 

Moderate to low liquefaction potential 
Out of service for 2 days 

E3 Fernbridge Substation 

MMI IX 

High liquefaction potential 
Out of service for 3 days 

E4 Humboldt Bay Power Plant and Substation 

MMI IX 

High potential for liquefaction 
Tsunami run-up zone 
Out of service for 7 days 

At present, the Humboldt Bay Power Plant exclusively generates power from fossil fuel. 
Previously, power was generated from nuclear energy, however the nuclear power plant 
with its fuel rods now remains idle. 

The Humboldt Bay Power Plant is in the path of a tsunami and would immediately be 
shut down before its arrival. The earthquake will damage the plant before the tsunami 
arrives. 

Two fuel tanks and one water tank are vulnerable to earthquake forces. The water tank 
is a single wall steel tank with a 300,000 gallon capacity, and is used in producing 
electricity. The fuel tanks have cellular construction and are less vulnerable than the 
water tanks; however, a tsunami could spread spilled fuel. 

107 



NORTH COAST SCENARIO 

Photo E-1 shows the power plant and part of the substation, and the cooling water 
channel which will be a free face during liquefaction. Damage to the equipment at the 
Humboldt Bay Power Plant substation will be substantial in this scenario earthquake. 




Photo E-1 Humboldt Bay Power Plant, cooling water channel and substation. 



E5 



Eureka Substation 

MMI VIII + 

Out of service for 2 days 

The strong shaking will damage the high voltage equipment at this substation. 



E6 



Fairhaven Power and Louisiana Pacific Power Plants 

MMI IX 

High potential for liquefaction 

In tsunami run-up zone 

Out of service for an extended period 

The Fairhaven and Louisiana Pacific Power plants are on the Samoa Peninsula on the 

western side of Humboldt Bay. These privately owned power plants sell electricity to 

PG&E. These are in the direct path of the tsunami, and will be seriously damaged. 



108 



NORTH COAST SCENARIO 

E7 Areata Substation 

MMI IX 

High potential for liquefaction 
Out of service for more than 3 days 

This substation is on the corner of Sixth and I streets, and the soils in this area are 
susceptible to liquefaction. 

E8 Janes Creek Substation 

MMI VIII + 

Out of service for 1 day 

E9 Trinidad Substation 

MMI VIII + 

Out of service for 1 day 

E10 Big Lagoon Substation 

MMI VIII + 

Out of service for 1 day 

E11 Substation at Orick 

MMI IX 

High potential for liquefaction 
Out of service for 3 days 

E12 Substation near Smith River, north of Crescent City 

MMI IX 

Moderate to low liquefaction potential 

Out of service for 2 days 

Strong ground shaking will damage the high voltage equipment. 

E13 Transmission Lines to Oregon 

MMI VII 

Potential for landslides 

Out of service for 2 days 

Seismically induced landslides will disrupt the northern of these two lines near Gasquet. 



109 



NORTH COAST SCENARIO 

NATURAL GAS 
General Characteristics 

Natural gas is supplied to Humboldt County by Pacific Gas & Electric (PG&E). The principal facilities 
and routes of the major gas transmission pipelines serving the area are shown on Maps EGP-1 and 
EGP-2 and AR. The planning area no longer has above-ground gas holders. Selected locations and 
facilities were reviewed in the field for earthquake damage potential. The principal areas in 
Humboldt County that have natural gas service available through PG&E are the same as those listed 
in Table E-1 (refer to Electric Power chapter). 

In Del Norte County, Crescent City is served mainly by the two distributors Blue Star Gas and 
Suburban Propane. They provide about 97 percent of the service to the area, which they evenly 
split. The remaining 3 percent is provided by Farrelgas, a company based in Brookings, Oregon. 
Propane is trucked into the city for further local distribution. Blue Star Gas has a limited 
underground distribution system for the downtown area from their storage tanks. Blue Star's 
propane storage tank terminal in Crescent City consists of three tanks with capacities of 1 1 ,000, 
1 7,000, and 30,000 gallons. Blue Star's remaining service and all of Suburban Propane and 
Farrelgas is delivered by truck to various local clients which include businesses, industry, and private 
residences. The reader should refer to the chapter on Petroleum Products for a discussion of typical 
storage tank performance. 

Gas Field Operations 

There are two commercial gas fields in the planning area, both in southwest Humboldt County. The 
Table Bluff gas field is about 2 to 3 miles (3 to 5 km) north-northwest of Loleta. This field consists 
of five wells, and produced gas from 1 962 until the field was abandoned in 1 968. 

The Tompkins Hill gas field is the only currently active gas producing field in the planning area and 
has been operating since 1 938. The field is on an east-west trending ridge named Tompkins Hill in 
Township 3 North, Range 1 West, Sections 14-17 and 20-24, with the west end of the field about 
2 miles (3 km) north of Fortuna. Currently, this field consists of 34 active and 5 inactive wells 
which produced 1,760,000,000 cubic feet of gas in 1993. The gas is sold to PG&E, where a 
portion is used to partially fuel the Humboldt Bay Power Plant and the rest is distributed to utility 
customers in the Eureka-Arcata-McKinleyville area. The gas is shipped from the field in a 4 to 6 inch 
steel pipeline, which connects to the 1 2 inch pipeline operated by PG&E, that runs along the east 
side of Humboldt Bay. 



110 



NORTH COAST SCENARIO 

The Little Salmon fault passes through the field, running diagonally across the southwest corner of 
section 1 5, across the northeast corner of section 22, diagonally across section 23 and through the 
southeast corner of that section. 

Seismic Considerations 

While gas supply systems are typically rugged and have performed well in past earthquakes, some 
damage has occurred, particularly to older components of transmission and distribution systems. 

Transmission systems carry gas from production or storage fields in high pressure lines. This 
system may include terminals, compressor stations, and pressure limiting stations. Transmission 
pipelines can survive strong shaking, but can be damaged by permanent ground deformation. For 
example, during the 1971 San Fernando earthquake (M6.7), several pre-1940 gas transmission lines 
suffered numerous breaks in an area that experienced surface fault rupture. The lines ranged from 
12 to 26 inches in diameter and were of welded steel construction. One 6 mile (10 km) length of 
pipeline had 52 breaks (NOAA, 1973). 

The typical gas distribution system consists of a vast network of relatively small diameter (2 to 8 
inches) underground lines and related above ground control facilities. Major earthquake 
vulnerabilities of distribution systems include permanent ground deformation and strong shaking 
affecting non-ductile distribution lines that are of older design or may have deteriorated with 
corrosion. New arc-welded steel lines and plastic lines are more ductile than the old lines and 
perform better. If permanent ground deformations occur, such as those caused by liquefaction, the 
old lines generally are much more vulnerable than the new lines, but both can be damaged. 

During the 1989 Loma Prieta earthquake (M7): 

"The gas transmission lines and large diameter distribution mains experienced only three leaks 
due to the earthquake. Unstable soil in the Marina District of San Francisco caused damage 
that resulted in the replacement of approximately 10 miles (16 km) of cast iron and steel 
distribution mains with polyethylene plastic pipe. Also in the Marina, 1,500 services to 5,400 
individual meters were replaced in less than 5 weeks. Three miles of distribution mains were 
replaced in Los Gatos and Watsonville. Other damage was scattered and minor. 

PG&E restored service to over 150,000 customers whose gas service had been turned off. A 
total of 1,100 service personnel participated in the relighting process, including 400 from 
other utilities in the west. Within a week, service was restored to all customers with 
undamaged piping" (EERI, 1990). 

Gas lines can be damaged where they enter buildings or connect to water heaters. This sometimes 
causes localized outbreaks of fire as they did in the Marina District of San Francisco in the 1 989 
Loma Prieta earthquake. 

Ill 



NORTH COAST SCENARIO 



In the 1992 Landers and Big Bear earthquakes of June 28, 1992 (M7.5 and M6.6): 

"Most gas service damage from the earthquake occurred in four mobile-home parks and 
a low-income housing project. About 60 percent of the damage to house gas lines 
occurred between meters and mobile homes when the homes shifted off their supports. 
Many water heater connections failed. Some water heaters slipped off their stands, fell 
out of cabinets, and broke restraining straps" (Lund, 1994). 



During the 1992 Petrolia earthquake (M7.0): 

"Gas mains responded well in bridge structures even though the bridges were subject to 
slight displacement. There were no underground gas leaks in the distribution system; 
however there were some small leaks at meter risers due to falling debris. In Rio Del 
and Fortuna, approximately 50 service connections were shut off due to structural 
damage or leaks" (EERI, 1992a). 



The fire in Scotia that burned the Post Office and General Store apparently was caused by the 
breaking of a gas line. 

Relative to the 1994 Northridge earthquake (M6.7), two reports provide valuable insights on damage 
patterns to natural gas transmission lines: 

1 . "The natural gas supplier experienced about 1 50,000 outages, of which approximately 

1 30,000 were unnecessary customer initiated closures. Preliminary reports on February 2 
indicates that there were a total of 1 ,377 breaks and leaks in the piping system. 
Approximately 489 occurred in distribution lines, 35 in transmission lines, with the 
remaining 853 in service connection lines. The distribution systems consist of steel and 
plastic with pressures limited to 60 psi. No leaks or damages were suffered by the plastic 
piping. Restoration of customer service is very time consuming because of the need for 
gas service personnel to check internal gas piping and gas appliances before turning on the 
service. The transmission system service consists of steel pipe varying in diameter from 
1 2 to 30 inches. The most visible failure occurred along Balboa Boulevard where a 22 inch 
line suffered two breaks, one in tension and the other in compression. These failures were 
located in parallel ground rupture zones crossing roughly perpendicular to the pipelines. 
The fire occurred at the northerly break where the gas pipe separated approximately 9 
inches. In the Aliso Canyon Gas Storage Field, located in the Santa Susana mountains 
north of Granada Hills, a break occurred in a 10 inch gas line leaving the field, and there 
was damage to above ground pipe supports, displacement of runs of injection and 
withdrawal gas lines, and structural damage to fan units used to cool compressed gas prior 
to injection into the storage wells. The gas supply from Aliso Canyon was interrupted for 
approximately 5 days" (EERI, 1994). 

2. "...ground deformation across Balboa Boulevard between Rinaldi and Lorillard streets... was 
responsible for breaks in one gas transmission and two water trunk lines. ...Gas escaping 
from Line 1 20 was ignited by sparks from the ignition system of a pick-up truck that had 
stalled in the area of tensile ground deformation flooded by the ruptured trunk lines. The 
gas fire spread to adjacent properties, destroying five houses and partially damaging 
another structure" (O'Rourke and others, 1994). 



112 



NORTH COAST SCENARIO 

The propane storage tank terminal in Crescent City is outside the postulated tsunami run-up area. 
However, it is in an area with an expected MMI VIM + which indicates that it will be subject to 
heavy ground shaking and potential damage. 

Planning Considerations 

Sources of natural and propane that are outside the strongly shaken areas are not expected to be 
damaged or impaired by the scenario earthquake. Humboldt County is supplied by gas from 
Sacramento Valley and from Tompkins Hill gas field. Both transmission lines will be damaged where 
they cross the Little Salmon fault (Map EGP-1). The extent of damage is difficult to predict because 
high pressure transmission lines are typically stronger and more rugged than distribution lines, but 
for planning purposes, the possibility of breaks and leaks at these locations must be considered. 
There are fewer lines involved in transmission than in distribution, and repairs to transmission 
facilities generally take less time. 

Numerous breaks and leaks will occur in the local distribution system throughout the strongly 
shaken area, especially where ground failure occurs as a result of liquefaction. 

While gas supplies to most of the Humboldt County planning area will be restored rapidly, 

distribution systems in areas of fault rupture or liquefaction could be without gas for several 

weeks. Restoration of the distribution system is a gradual process as described in the following: 

"Unlike electricity, which can usually be turned off and on at will, the restoration of gas 
service is an expensive and time consuming task. If a pipeline is broken, or part of a 
distribution network loses all pressure, every customer being supplied from that network must 
individually shut down before repressuring can begin. To prevent explosions, the entire 
system of mains, feeders, and service lines in the affected area must be purged before pilot 
lights can be relighted and service restored. In addition, extensive gas leak detection surveys 
may be needed, using flame ionization equipment throughout the affected area" (LNG Task 
Force, 1980). 

Planning Scenario 

For local areas within the MMI VIM + and IX zones, gas service will be disrupted by the earthquake. 
The typical outage time will be 1 to 2 days, except in areas subject to ground failure. In areas 
faulting or liquefaction outages may last up to several weeks. We expect the maximum length of 
gas outage in areas not subject to ground failure to be 3 to 5 days. 

As indicated in the Water Supply chapter, we expect fires to break out in the downtown areas of 
Eureka, particularly where older wood frame buildings are clustered in areas of liquefaction. Local 
fires caused by gas line breaks will occur in other communities, particularly those experiencing 

113 



NORTH COAST SCENARIO 

MMI VIII or greater shaking. The damage to water supply services will make fire fighting difficult in 
these areas. Unless emergency water supply is immediately available, fire control could take from 2 
to 3 days. 

In Del Norte County, we expect local customer service to be disrupted by broken storage tank 
connections. We also expect several fires to result from this damage. Unless the winds are strong 
the fires most likely will be confined to the structure of origin. 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Repair times can be lengthy because of the testing, repressurizing, and 
relighting procedures that must be followed. Approximately 2 weeks would not be unusual, and 
outside help from within the company or provided through a mutual aid arrangement often is 
required. Locations of storage and related facilities are shown on Maps EGP-1 and EGP-2 and AR. 

MAP NO . GAS FACILITIES 

G1 Transmission Line from the east 

MMI VII 

Potential for landslides 

Open 

G2 Transmission Line through the Van Duzen River Valley 

MMI IX 

Moderate to low liquefaction potential 

Open 

G3 Transmission Line through Fortuna 

MMI IX 

Moderate to low liquefaction potential 
Open 



114 



NORTH COAST SCENARIO 

G4 Tompkins Hill Gas Field and Regulator Station 

MMI VIII + 

Little Salmon fault rupture 

Potential for landslides 

Closed more than 3 days 

Of the 39 active and inactive wells in the field, 1 7 are on the northeast side of the Little 

Salmon fault or very near the fault. The casings of these wells will be sheared by 

rupture along the Little Salmon fault, making the wells inoperable. Nine of these wells 

are also on active landslides. On the southwest side of the Little Salmon fault, five of 

the remaining 22 wells are on existing landslides which will reactivate, or on locally 

steep slopes that are subject to slope instability. These 5 wells will suffer damage to 

shallow or surface well components and piping, making them inoperable. Additionally, 

there will be damage to the gas collection piping at the field by ground shaking and 

deformation, causing a disruption of gas transmission from the field, a release of gas, 

and possible fires. 

G5 Tompkins Hill Road, east line 

MMI VIII + 

Little Salmon fault rupture 
Closed for 3 days 

G6 Humboldt Hill, east line 

MMI VIII + 

Potential for landslides 
Closed for 2 days 

G7 South of Tompkins Hill Overhead, west line 

MMI IX 

High liquefaction potential 
Closed for 3 days 

G8 Tompkins Hill Overhead, west line 

MMI VIII -h 

Little Salmon fault rupture 
Closed for 3 days 



115 



NORTH COAST SCENARIO 

G9 Elk River Valley, west line 

MMI IX 

High liquefaction potential 
Closed for 2 days 

G10 Distribution Lines, Eureka 

MMI VIII + to IX 

Low to high liquefaction potential 
Closed for over 3 days in a few local areas 

Strong shaking will cause breaks in service gas lines in Eureka in the areas of 
liquefaction bordering the bay. There will be some post-earthquake fires due to service 
line breaks. 

G1 1 Distribution Lines, Areata 

MMI VIII + to IX 

Low to high liquefaction potential 
Closed for over 3 days 

Strong shaking and liquefaction will cause breaks in service gas lines in the western part 
of Areata. There will be post-earthquake fires due to service line breaks. 

G12 Crescent City Propane Tanks 

MMI VIII + 
Closed for 2 days due to damaged piping and possible leaks 



116 



NORTH COAST SCENARIO 

WATER SUPPLY FACILITIES 
General Characteristics 

Water supply, along with electric power and transportation, is one of the most critical lifeline 
systems for rapid post-earthquake response and recovery efforts. If major damage has occurred to 
any municipal or regional water supply system during an earthquake, it is essential that the system 
be restored as quickly as possible (Lagorio, 1994). The potential loss of water supply to urban areas 
is one of the most important concerns to be faced by municipal and county jurisdictions. 

Major water supply systems and their primary sources for the conveyance of water to local 
communities in the planning area are shown on Maps W-1 and W-2. The two principal water supply 
agencies in Humboldt and Del Norte counties and their sources of water are listed in Table W-1 . We 
visited representative dams, reservoirs, river intakes and storage tanks of both agencies. The 
remaining smaller communities throughout the planning area rely primarily on wells for water. 

Humboldt Bav Municipal Water District (HBMWD). Humboldt County 

The main water supply for the HBMWD system which serves 70,000 people comes from the Mad 
River whose source is in the Trinity National Forest approximately 65 miles (105 km) southeast of 
Eureka. HBMWD supplies approximately 50 million gallons of water per day to its service area, 
including the pulp mills on Samoa Peninsula. The major storage area for the water is Ruth Lake, 
impounded by Matthews Dam which is a closely monitored earth filled dam, 50 miles (80 km) 
southeast of Eureka (Photo W-1). 

Downstream, with the riverbed acting as a filtration system, six pumping stations are spaced apart 
along the Mad River near Essex, 10 miles (16 km) north-northeast of Eureka. A booster pump 
station at Janes Creek supplies water to the City of Areata and the industrial complex along the 
Samoa Peninsula. Areata gets its water from the HBMWD. Two 42 inch diameter pipelines extend 
from Janes Creek south to the Samoa Peninsula and a small pipeline extends across Humboldt Bay 
near the Bayshore Mall. A one million gallon steel storage tank is on the Samoa Peninsula near 
Fairhaven. 

Eureka water comes through 24 inch steel pipelines from the Mad River to a 20 million gallon 
storage reservoir and water treatment plant near Sequoia Park. An elevated 500,000 gallon water 
tank and a 1,000,000 gallon ground level steel tank serve residential areas along Harris Street north 
of the Sequoia Park Reservoir. A 500,00 gallon ground level steel tank serves the Lundbar Hills 
area. The 20 million gallon storage reservoir will be out of service till late 1995 for repairs. Also, 



117 



NORTH COAST SCENARIO 

TABLE W-1 
WATER SERVICE AGENCIES AND SOURCES OF SUPPLY 



DISTRICT 


COUNTY 


CITIES SERVED 


MAJOR SOURCES 


Humboldt Bay Municipal 
Water District (HBMWD) 


Humboldt 


Areata 
Blue Lake 
Eureka 

McKinleyville 
Samoa Peninsula 


Mad River 
Ruth Lake 


Crescent City Water Supply 
District (CCWSD) 


Del Norte 


Crescent City 


Smith River 




Photo W-1 



Matthews Dam and Ruth Lake. 



118 



NORTH COAST SCENARIO 

the 24 inch line broke north of Eureka and was out of service for a few days. The 500,000 gallon 
elevated tank currently is limited to 250,000 gallons for earthquake safety reasons. 

Crescent Citv Water Supply District (CCWSD). Del Norte County 

The main water supply for the CCWSD is pumped from the bed of the Smith River, 8 miles (13 km) 

north of Crescent City. 

All other communities within Humboldt and Del Norte counties are supplied by wells or other water 
supplies local to those communities. 

Seismic Considerations 

After an earthquake, water supply becomes a particularly vital resource to every community, as it is 
required for emergency firefighting, as well as for drinking, sanitation, medical emergencies, 
commercial functions, and industrial operations. In addition, prolonged water outages, even for a 
few days, can have serious economic and social consequences for a community. In these terms, 
strategies for the post-earthquake recovery of water supply systems must be a critical element in 
pre-disaster planning efforts of every community in areas of high seismicity. 

During major earthquakes in the past, typical damage patterns to water supply system components 
have been documented as follows: 

1 . Damage to sources of supply: dams, reservoirs, main storage tanks, intakes at rivers* 

2. Damage to transmission facilities connecting sources of supply to local communities: 
aqueducts,** canals 

3. Damage to treatment facilities* 

4. Damage to distribution system networks: localized storage tanks, pumping stations,* 
valves/mains 

* Also dependent on availability of electric power. 
** Includes open channels, tunnels, and large diameter steel or concrete pipe. 

Damage to, and disruption of sources of supply can include dam, reservoir, or major storage tank 
failure. In the 1971 San Fernando earthquake (M6.7), the upstream face of the Lower Van Norman 
Reservoir slumped and almost resulted in a catastrophic dam failure. This 20,500 acre-foot capacity 
reservoir had to be drained on an emergency basis. Had dam failure occurred, thousands of homes 
and tens of thousands of people living in the area below the dam would have been flooded and the 
loss of life would have been high. 



119 



NORTH COAST SCENARIO 

Significant disruption of water supply and delivery systems during an earthquake may also be 
caused by electrical power outages that impact service to pumping stations and river intake 
facilities, essentially closing down operations. The availability of emergency generators then 
becomes critical. 

Historic accounts of the 1932 Eureka earthquake (M6.2) document damage to tall industrial brick 

chimney stacks, a steel elevated water tank, and the electric power system (Sparks, 1936). 

Similarity between the 1932 earthquake and the 1954 Eureka earthquake (M6.5) has been noted in 

other documents. In the 1954 earthquake, an MMI VII was recorded in Eureka. Damage to 

elevated water storage tanks and water supply lines was documented as follows: 

"There are many wooden elevated water tanks throughout the rural areas, and some at 
sawmills. The tank at the Valley Flower Cooperative Creamery near Ferndale is the only 
one known to have collapsed. A large wooden elevated water tank at a sawmill was 
reported to have sustained minor damage. ...The results of inspections of four steel 
elevated water tanks revealed that the only one damaged was at the plant of the Eureka 
Redwood Lumber Company. Six of its eight top panel rods were broken, and there were 
several slack rods elsewhere. The tank was in poor repair, as was indicated by 
excessive rusting. The present owners state that, as one of the employees recalls, 
similar damage occurred in 1932. ...The Pacific Gas and Electric Company's tank 
showed evidence of high stresses at anchor bolts and in the rods. The other two tanks 
showed no evidence of high stress. 

The Eureka water supply comes [in 1 954] from the Sweasey Dam [which no longer 
exists] on the Mad River; the dam is about ten miles east of the city. The Division of 
Water Resources of the California Department of Public Works inspected and reported 
no damage to the 60 foot high variable radius arch concrete dam, which was built in 
1938. They also reported that the dam was designed for an earthquake force of 10 
percent of gravity. 

The water supply line to Eureka was damaged in three places [marked on Map W-1], with 
possible minor damage elsewhere. Leakage was considerable, but water continued to flow. 
The supply line consists of 36-in. wood-stave or 30-in. steel pipe, depending on the locality. 
There was damage north of Areata when the wood-stave pipe pulled partly out of a concrete 
block; this location was a transition section between wood-stave (above ground) to steel pipe 
(below ground) to allow roadway passage. ...The central break, at Ganno Slough, occurred in 
a marsh area where the steel pipe went under a creek. Comparable damage occurred in a 
similar situation at the third rupture, just east of Eureka at Freshwater Slough. Repair to this 
last break was particularly difficult and finally required laying pipe on a new bridge crossing 
the creek; cost of this repair was about $25,000 and required that the pipeline be shut down 
for forty-eight hours. In the marsh areas the steel pipe was encased in concrete, laid 
underground, and supported on piling. 

Damage was done also to the main reservoir in Eureka, which consists of an excavation 
plus embankment, the embankments being constructed of earth removed from the 
excavation. The reservoir, divided into two compartments by a structural reinforced 
concrete wall, has a capacity of 20,000,000 gallons. The interior surfaces are lined 
with concrete reinforced mesh. The reservoir was leaking prior to the earthquake, and 
after the shock the leakage jumped to an estimated 1 ,700,000 gallons per day" 
(Steinbrugge and Moran, 1957). 



120 



NORTH COAST SCENARIO 

The main difficulty in determining the extent of damage to distribution lines is that leaks may not be 
located until water pressure is restored. For this reason, it may take days or weeks to totally repair 
damage in densely populated, heavily impacted areas. Fresh water for domestic purposes often has 
to be supplied by tanker trucks or temporary above ground distribution lines during the immediate 
emergency and recovery period following a major earthquake. 

The 1 954 Eureka earthquake produced 30 breaks in the city's water mains (Louderback and others, 
1955). Total cost of repairs to the water supply, storage, and distribution systems of Eureka was 
estimated at $44,000. A rolled earth fill dam, 50 feet high, on Jolly Giant Creek and owned by the 
City of Areata, was undamaged according to the California Division of Water Resources. "There 
were four minor breaks in the Areata water system, and because of temporary power failure the 
pumps were not able to keep up water pressure" (Steinbrugge and Moran, 1957). 

In Alaska during the 1 964 earthquake, a short documentation of tsunami damage to utility systems 

on Kodiak Island offers some useful data relative to the seismic performance of fire hydrants 

(Richardson, 1973): 

"Utilities were not materially affected by ground shaking, but were damaged by the 
tsunamis. A number of power poles and fire hydrants were broken off in the waterfront 
area, and sewer outfalls were washed away." 

The 1 992 Petrolia earthquake (M7) produced the following impacts to water supply systems and fire 

fighting capacities in the Humboldt County area (Varner and Varner, 1992): 

"The most significant loss of water service occurred in the City of Rio Dell when their 
8-inch water main broke at the rise at the abutment of the southbound Eel River Bridge. The 
break caused the supply tanks to drain, leaving the city without a water supply. An 
emergency potable supply was provided by the American Red Cross, National Guard, and 
Anheuser Busch, Inc. Fire protection was supplied by contractor tank trucks. Water supply to 
the city was restored four days later on April 1 9th. 

Scotia, across the Eel River from Rio Dell, has separate water supply systems for 
domestic and fire protection. The fire protection (e.g., water) system was damaged and 
was inoperable. A fire destroyed Scotia's four-store shopping center after the second 
earthquake. The California Office of Emergency Services (OES) provided the town with 
a portable piping system and pump which was installed by the Scotia Volunteer Fire 
Department. It was available for service on April 28th. There was no reported damage 
to the domestic water system." 

The recent 1994 Northridge earthquake (M6.7) in the Los Angeles area of Southern California offers 

additional insights on the seismic performance of water supply systems: 

"The earthquake disrupted all four pipelines from Northern California which serve the 
Santa Clarita and San Fernando Valleys and supply three water treatment plants. The 
pipelines are steel with diameters ranging in size from 54 to 1 20 inches. All suffered 
breaks but were repaired in two to ten days. The treatment plants have capacities of 
25, 550, and 600 mg per day. They received minor damage, such as settlement around 

121 



NORTH COAST SCENARIO 



the plants, leaks at construction joints, leaks in plastic chlorine solution lines, and 
damage to wooden baffles in the basins. Supply was available in most areas from 
storage and other regional sources, but was not available to customers because of the 
damage to the distribution system. 

The most significant damage to the distribution pipeline network was within the 
epicentral area. Over 1,200 leaks in water lines and service connections in the San 
Fernando Valley and approximately 300 leaks in the Santa Clarita Valley have been 
identified as of February 8th [1994]. Pipes, some previously weakened by corrosion, 
were broken in compression and tension, most likely because of permanent ground 
deformations. 

An unusual concentration of eight systems occurred on Balboa Boulevard in Granada 
Hills. Located in the streets were three gas, three water, two sewer and one oil 
underground lines; 24.5 kV and 4.8 kV power, telephone, and cable TV overhead lines; 
and ornamental street lighting. Ground movement caused the breakage of some of the 
underground pipelines; a fire occurred that ultimately burned the overhead lines and five 
homes. ...The repairs were time consuming and required draining prior to repair, the 
repair itself, filling the pipe for testing, and chlorination. Invariably another leak was 
observed, after which the process was repeated, sometimes several times. ...There was 
damage to tanks which included rupture of inlet-outlet piping, buckling at the back of 
the tank (elephant's foot), shell buckling, ground settlement, and roof damage. 

Emergency water supply was provided by bottled water, beer and soft drink beverage 
companies, and water agencies provided water using rented tanker trucks. Mutual aid 
was provided by almost a dozen water agencies throughout the state and contractors 
familiar with water utility work. A number of fire department engine pumpers were used 
to pump water between fire hydrants to higher elevation service zones" (EERI, 1994). 



During the 1 989 Loma Prieta earthquake (M7), the Rinconada Water Treatment Plant (80 mgd 
capacity) suffered damage to three of its up-flow clarifiers. Wave action and differential movement 
damaged the interior metal structure. The fourth clarifier was empty at the time. The plants 
operated at 50 percent capacity until repairs could be made (EERI, 1990). 

The supply of water to urban centers is one of the most important concerns facing local 
jurisdictions. Aqueducts, pumping stations, distribution lines and water treatment facilities have 
been damaged in past earthquakes by both ground displacement and shaking effects. 

Planning Considerations 

Firefighting efforts are easily hampered during the first 24 to 72 hours by blocked streets, 
insufficient personnel, structurally damaged fire stations, and the lack of water or power. Power 
outages affect water supplies wherever pumping is required for distribution. Gravity flow systems 
are better able to withstand power outages. 



122 



NORTH COAST SCENARIO 

We expect the water systems within the planning region to suffer some damage. In areas of intense 
shaking or ground failure, pipeline breaks will be numerous. Breaks will be most common where 
water lines are corroded or otherwise deteriorated with age. Treatment facilities, structures, and 
equipment with poor seismic design will suffer damage and impairment. 

The components of each water supply system-the source, aqueducts and transmission pipelines, 
local storage reservoirs, pumping stations, treatment facilities, and distribution lines-must be viewed 
in the context of the entire system and its performance. Impairment of any major element can 
seriously compromise the performance of the entire system. Effects on other systems, such as 
electric power and waste water treatment, must also be kept in mind. 

It is essential that water agencies examine their transmission and distribution systems in detail to 
identify areas and facilities most likely to be impaired. Existing maintenance programs should be 
reviewed and new programs established to progressively upgrade facilities of questionable seismic 
resistance, particularly in areas of high vulnerability. 

Stocks of materials and equipment to make emergency repairs must be readily available at all times. 
Mutual aid arrangements are extremely important in these cases, and might be especially important 
in this rural and relatively isolated area. The scale of earthquake damage to water lines will be much 
greater than non-seismic breaks and leaks normally experienced. Thus, water agencies must 
maintain an adequate stock of critical repair materials, that have long lead times for procurement. 

In areas having a significant possibility of water outage, plans need to be developed for providing 
water via ground transportation. Generally, water supply cannot be restored to an area where 
sewer lines are still broken or not functioning. Emergency power sources must be provided for 
those vital elements (e.g., pumping stations) that lack a backup power supply. 

Chlorine is applied at the Eureka treatment plant near Sequoia Park. Damage to the chlorination 
equipment or to the tanks could result in a hazardous material spill or leak. 

Planning Scenario 

The water supply from the HBMWD and CCWSD intake structures along the Mad River and Smith 
River, respectively, will be reduced due to power outages and pipe breaks caused by liquefaction 
ground failures. 



123 



NORTH COAST SCENARIO 

In areas of intense shaking (e.g., MMI IX) or ground failure, two to four mains break in every 
residential block will be common where nonductile cast iron or asbestos cement pipe exists. In 
these areas, repairs of water supply lines could be delayed because of contamination from broken or 
severed sewer lines in the vicinity. 

In areas of strong shaking (e.g., MMI VIII and greater) flat bottom water storage tanks will have 

failures sufficient to cause a loss of water. According the NAS (1973): 

"The behavior of large liquid storage tanks during earthquakes has an importance far beyond 
the mere economic value of the tanks and contents. If, for instance, a water tank collapses, 
as it did during the 1 933 Long Beach earthquake (M6.3), the loss of public water supply can 
have serious consequences." 

Typical damage patterns for large liquid storage tanks are: 

1 . Total collapse 

2. Roof buckling 

3. Damage to the connection between the roof and the shell 

4. Shell wall buckling 

5. Separation of shell from bottom plate (with loss of contents) 

6. Separation in pipe-to-tank connections (with loss of contents) 

Because of failures in local water distribution systems, many communities will be asked to use 
emergency supplies, boil their water, or take other measures against contamination for a week or 
longer. 

For disaster response planning, authorities should expect localized fires to break out in the 
downtown areas of Fortuna, Eureka, Areata, Crescent City, and in areas where older wood frame 
buildings are clustered. Because of damage to water supply and distribution lines, difficulties will be 
experienced in fighting fires in these areas. Unless an emergency water supply is immediately 
available, complete fire control will take up to 48 hours. Owing to the public's crucial need for 
water, it is assumed that highest priorities will be given to the restoration of electric power to all 
major pumping and treatment facilities. 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Locations of water supply facilities are shown on Maps W-1 and W-2. 



124 



NORTH COAST SCENARIO 

MAP NO . WATER SUPPLY FACILITIES 

W1 Ruth Lake/Matthews Dam on the Mad River in Trinity County 

MMI VIII 

Open 

Only minor damage is expected at this earth fill dam (Photo W-1), which is 50 miles (80 

km) southeast of Eureka. 

W2 Fields Landing 

MMI VIII + 

Little Salmon fault rupture 
Closed for an extended period 
The water line to the College of the Redwoods will be disrupted by faulting. 

W3 Lundbar Hills and City of Eureka Tanks 

MMI VIII + 

Closed for more than 3 days 
Damage to both ground level tanks is expected by buckling due to sloshing. 

W4 20 Million Gallon Reservoir and Filtration Plant, Eureka 

MMI VIII + 

Closed for 2 weeks 

Fed by the HBMWDs 24 inch line, this facility is expected to suffer extensive damage 

due to strong ground shaking. 

W5 Elevated Tank and Ground Level Tank, Eureka 

MMI VIII + 

Closed for more than 3 days 

Serious damage to the elevated tank may include collapse. The ground level tank will 
also be damaged. 

W6 Lines across Humboldt Bay 

MMI IX 

High liquefaction potential 
In tsunami inundation zone 
Closed for more than 3 days 

The two 42 inch lines crossing Humboldt Bay on pilings from the Samoa Peninsula will 
suffer serious damage, and will be out of service for several weeks. 



125 



NORTH COAST SCENARIO 

W7 Fairhaven Water Tank 

MMI IX 

High liquefaction potential 
In tsunami run-up zone 
Closed for an extended period 

The one million gallon storage tank near Fairhaven is expected to be destroyed by the 
earthquake and tsunami. 

W8 Main Line at Ryan Slough 

MMI IX 

High liquefaction potential 
Closed for more than 3 days 

The 24 inch line crossing Ryan Slough and Freshwater Slough is expected to suffer 
severe damage as it did in the 1 954 earthquake. 

W9 Main Line south of Sunny Brae 

MMI IX 

High liquefaction potential 
Closed for more than 3 days 

The 24 inch line will be damaged between Sunny Brae and Bayside, as happened in the 
1954 earthquake (refer to Steinbrugge and Moran, 1957). 

W10 Main Line northeast of Areata 

MMI IX 

High liquefaction potential 
Closed for more than 3 days 
The line will be damaged near Korbel, as happened in the 1 954 earthquake. 

W11 Ranney Wells and Pumps near Essex 

MMI IX 

Low to moderate liquefaction potential 
Closed for more than 3 days 

The Mad River contains 6 wells and 15 pumps. Electrical power will be lost and the 
tower structures will be damaged. 



126 



NORTH COAST SCENARIO 

W12 Storage Tanks (1,000,000 and 1,500,000 gallons). Crescent City 

MMI VIII + 

Closed for more than 3 days 

There will be elephant foot buckling due to sloshing of water in these ground level tanks. 

This will be accompanied by broken connections. These effects will result in serious 

losses of water for the city. Other damage could occur to booster pumps, the 

chlorination facility, and other parts of the water system. 

W13 Elevated Tank (50,000 gallons), Crescent City 

MMI VIII + 

Closed for 1 week 

This tank will be seriously damaged and could collapse. 

W14 Ranney Wells and Pumps in the Smith River 

MMI IX 

High potential for liquefaction 
Closed for more than 3 days 
Expect loss of electrical power and damage to the tower structure in the riverbed. 



127 



NORTH COAST SCENARIO 

WASTE WATER 
General Characteristics 



The major waste water treatment jurisdictions in the planning area are: 

1 . Elk River Sewage Treatment Plant, Eureka 

2. Areata Waste Water Treatment Facility, Areata 

3. Water Pollution Control Facility, Crescent City 



Major agencies were visited and selected facilities in Humboldt and Del Norte counties were 
inspected for potential earthquake damage. 

The major treatment plants are located along bay margins as shown on Maps W-1 and W-2. Other 
small facilities are located in interior regions of the planning area with outfall lines near rivers. Some 
of these systems involve gravity flow from the service area to the treatment plant with discharge in 
an outflow line, and others require pumping for all or part of their operation. 

In general, waste water treatment plants have only limited storage capacity either in the form of 
basins or holding ponds. If the treatment sequence cannot be restored before storage capacity is 
surpassed, it will be necessary to discharge waste water by using emergency methods of treatment 
to reduce the risk of pollution. The importance of storage capacity is significant after an 
earthquake. For example, during the 1992 Landers and Big Bear earthquakes (M7.5 and M6.6), 
considerable damage occurred within a secondary treatment plant of a regional waste water 
collection agency in the Big Bear Lake area. But with adequate storage, the biological treatment 
process was maintained, and there was no operational loss (EERI, 1992a). 

Damage and loss of power at critical facilities along the Bay margins, river delta regions, or other 
areas with a high potential for soil liquefaction, will necessitate sewage discharge directly into bays, 
deltas, rivers, or creeks at designated bypass locations. This will be accompanied by pollution at 
most waterways, which may pose a public health risk, depending on their location relative to 
populated areas. 

In some cities, it is common to find waste water collection lines in the same trench as water 
distribution lines. Damage to both lines may occur in areas of high ground shaking or ground failure, 
resulting in contamination of water supplies. This occurred in the City of Watsonville during the 
1 989 Loma Prieta earthquake (M7), where leakage from damaged sewage lines contaminated water 
supply distribution lines in the same trench. In general, the water supply cannot be restored in areas 
where sewer lines remain broken or are not functioning (refer to Water Supply chapter). 



128 



NORTH COAST SCENARIO 



Seismic Considerations 



The impact of an earthquake on waste water systems can be considered from three standpoints: 

1 . Damage to the collection systems 

2. Damage to treatment plants and outfalls 

3. Discharge of untreated or poorly treated sewage into holding ponds, rivers, or bays. 



Table VVW-1 shows the anticipated MMI and liquefaction potential for the scenario earthquake at 
sites of the major waste water treatment facilities. 

TABLE WW-1 
MAJOR TREATMENT FACILITIES 









LIQUEFACTION 


WASTE WATER TREATMENT FACILITY 


CITY 


MM INTENSITY 


POTENTIAL 


Municipal Treatment Plant 


Fortuna 


IX 


High 


Municipal Treatment Plant 


Ferndale 


IX 


High 


Elk River Sewage Treatment Plant 


Eureka 


IX 


High 


Areata Waste Water Treatment Facility 


Areata 


IX 


High 


Fisher Treatment Plant 


McKinleyville 


VIII + 


None 


Water Pollution Control Facility 


Crescent City 


VIII + 


None 



Waste water collection systems are primarily susceptible to earthquake damage as a result of broken 
underground pipelines. Lines typically made from relatively brittle clay, asbestos cement, or 
concrete pipe generally tolerate little movement without fracture. Damage tends to be greatest 
where permanent ground movements occur due to surface fault rupture, landslide, or liquefaction. 
The distribution of damage usually is similar to that suffered by other buried conduits, such as those 
carrying water, natural gas, and petroleum products. Because most sewer lines are not pressurized, 
broken lines are not readily detected unless blockage or severely restricted flow is experienced. 
Television cameras may be used to find cracks and broken lines. 

Data collected and reported by the National Academy of Sciences (NAS) after the 1 964 Great 

Alaska earthquake (M9.2) offer excellent insights on the impact that tsunamis had on sewer 

systems on poor soils in the City of Seward: 

"When the shaking had subsided, tsunamis started to come in, and for several hours 
they continued to damage as high as 31 feet above mean lower low water. The waves 
washed mud and silt into sewers and broken water lines, and the hydraulic pumping 
effect of continuous wave action packed mud into the lines. ...Along the bayside of the 
old townsite, large areas of ground slid into the bay, carrying away buried utilities, 



129 



NORTH COAST SCENARIO 



including the sewer outfall. The remaining ground cracked 100-200 feet inland in places, 
breaking sewer lines. Tsunamis and waves from slides and seiches pumped mud and silt into 
sewer lines and manholes; some manholes overflowed and mud rose above the inverts in 
others. The Clearview outfall traversed part of the lagoon area that sank several feet during 
the earthquake, and the bay end of the outfall was washed away by the waves" (NAS, 1973). 



A brief description of the damage to waste water treatment facilities at El Centro that occurred 

during the 1979 Imperial Valley earthquake (M6.4) follows: 

"The damage to the secondary clarifiers were primarily related to failure of the center 
wells and their impact on rake arms, drive shaft, skimmers and sludge withdrawal 
piping. The contents of the clarifiers experienced significant sloshing, with mixed liquid 
spills evident at both clarifiers in a northwesterly direction in line with the probable 
epicenter location. The north clarifier had more extensive damages than the south 
clarifier. In the north clarifier, the center well support frame failed causing the center 
well to drop onto the sludge collector rake arms. As the center well fell, it hit sludge 
withdrawal pipes, causing them to be pulled apart at the flexible hose connection elbow. 
Also sludge skimmers were pulled from their tracks and fell to the bottom of the tank" 
(EERI, 1980). 



During the 1971 San Fernando earthquake (M6.7), the sewage collection system was damaged in 
the Sylmar area, particularly in areas of fault rupture and permanent ground movement. In a 1 5 
square mile (39 sq. km) area that included Sylmar, over 126,000 feet of mainline sewer had to be 
reconstructed. The damage consisted of crushed and cracked pipe, broken (compression failure) 
and pulled (tension failure) joints, and damage to manholes. The latter consisted of shifting of rims 
as well as some cracking of the manholes themselves (NOAA, 1973). Treatment facilities have also 
been closed due to equipment failures and power outages. 

During the 1 989 Loma Prieta earthquake wave action at the 40 mgd Palo Alto Waste Water 
Treatment Plant caused fiberglass scum troughs to fall onto the sludge sweeping scraper in the 
bottom of a clarifier, causing it to jam. Two days were required to repair this clarifier, but 
fortunately the plant was back in operation in 2 hours because an empty clarifier was available 
(EERI, 1990). 

Regional waste water treatment plants in San Francisco and Oakland lost power but suffered no 
major structural damage during the Loma Prieta earthquake. There were some short time releases of 
sewage into San Francisco Bay and the Pacific Ocean. The Oakland plant lost commercial power for 
7 hours (EERI, 1990). 

Reports on the 1 992 Petrolia earthquake (M7) indicate that: 

"The water and sewer systems in Ferndale continued to function. In Fortuna, there was 
a power loss to a sewer pumping plant, but there were no reported sewer spills" (EERI, 
1992a). 



130 



NORTH COAST SCENARIO 

In the area impacted by the 1994 Northridge earthquake (M6.7) in southern California, two water 

reclamation plants that provide tertiary treatment of waste water were damaged: 

"Both plants lost power. The smaller plant did not have an emergency generator as it 
operates on a bypass of the main outfall sewer. At the large plant the emergency 
generator started automatically; however the operator was concerned about the 
generator's operation and shut it down. Although both plants lost power from 7 to 8 
hours, they did not lose their biological systems. The plants received minor damage, not 
significant enough to hinder operation when power was restored. Typical damage 
included dislodged sludge scrapers, broken auxiliary piping, broken windows, fallen 
ceiling tiles, and toppled warehouse supplies" (EERI, 1994). 

Planning Considerations 

Damage to collection systems will be similar to that experienced by water supply and distribution 
systems. Soil liquefaction in the poor ground areas will be a major source of damage (refer to Maps 
W-1 and W-2). To a much lesser extent, landslides, particularly at the end of a prolonged wet 
season, will cause damage to the collection systems in hilly areas. In areas of water outage or 
breaks in sewer lines, temporary facilities, such as the portable sanitary facilities used on 
construction sites, will have to be provided as they were after the 1971 San Fernando and the 1989 
Loma Prieta earthquakes. 

Buildings and other special structures found at treatment plants are usually earthquake resistive, 
particularly those built since the mid-1970s. In poor ground areas, large buildings and other major 
structures are normally on pilings and should survive without any major structural damage. Internal 
appurtenant piping and equipment are generally earthquake braced and intended for heavy duty. 
Building entry by pipes or conduits will be likely points of damage. Electric power outages will 
affect those treatment facilities and pumping or lift stations without emergency generators. 

Damage is likely in structures containing rotating equipment or other moving devices, with the 
damage being due to the wave action of sloshing liquids. Differential settlements will occur 
between underground piping and the connected buildings. The result of these differential 
settlements is to crack or break the pipe where it joins the building. This is a particular concern for 
pressurized lines (e.g., force mains). 

The quantity of waste water flowing to treatment plants will diminish immediately after the 
earthquake due to the closure of industrial plants and the reduction in the supply of fresh water. 

Treatment plant buildings, tanks, piping, machinery, and equipment are all subject to earthquake 
damage. If a treatment plant becomes inoperable, untreated sewage must bypass the plant and be 
dumped into holding ponds, creeks, rivers, bays, or the ocean. The discharge of raw or poorly 

131 



NORTH COAST SCENARIO 

treated waste water may be necessary, and will cause public concern. This should be reviewed 
beforehand with the appropriate environmental agencies. Public announcements should also be 
readied for distribution immediately after the earthquake. Review of the adequacy of chlorination 
tank storage, piping, and machine tie downs is of utmost concern. Adequate chlorine spill control 
programs are vital for all affected waste water stations. 

The time required for assessing damage and making repairs to a damaged collection system depends 
on the availability of personnel, equipment, and materials. In the relatively small area affected by 
the 1971 San Fernando earthquake, 90 miles (145 km) of sewer lines were surveyed by pulling 
television cameras through them. From a practical standpoint however, until water supply is 
restored, discharge of sewage into sewer connection lines will be significantly reduced. 

Planning Scenario 

Waste water lines that cross the Little Salmon fault will be severed and unable to carry waste water. 
Where major trunk lines are severed, open trenches may be needed to carry raw sewage for short 
distances. Alternatively, emergency planners will have to provide either temporary emergency 
housing arrangements for neighborhoods heavily impacted by the earthquake or temporary sanitary 
facility units. 

The flow capacity of the collection system in the poor ground areas as shown on Maps W-1 and 
W-2 will be reduced by 50 percent. The main collectors in these areas will be damaged, but will 
retain 75 percent of their capacity in those sections where gravity flow is possible. Main effluent 
lines of the Eureka, Areata, and Crescent City systems will be interrupted by breaks where they 
cross areas of liquefaction. Thirty days will be needed to restore service. 

Immediately after the earthquake, treatment plants without emergency power will shut down. 
Power requirements will diminish as the quantity of arriving waste water diminishes. Restoration of 
power will be a function of priorities. For instance, initial preference will be given to direct life 
support operations such as hospitals and water systems. This, in turn, will require emergency 
treated raw sewage to be discharged into holding ponds, creeks, rivers, and the bays for up to 1 
week. 

Depending on the number of tsunami waves and their height at the locations of the three treatment 
plants, there could be damage comparable to that experienced in 1 964 in Seward, Alaska. This 
included damage to the outfall, inundation of the plant and lines with silt and mud, ground failures 
that damaged utilities, and other problems noted earlier. 



132 



NORTH COAST SCENARIO 

Waste water treatment plants are generally located on poor ground that is highly susceptible to 
earthquake induced ground failure. This seldom results in damage to massive individual structures 
that are well designed and supported by piling or engineered fills. Instead, differential motion 
between structures and inlet and outlet lines often causes damage. In general, the contiguous trunk 
lines and outfalls also are in areas prone to ground failure. Gravity flow of waste water could be 
impaired by vertical deformation accompanying the earthquake, which will exceed the 4.5 feet 
(1 .4 m) uplift observed in the 1992 Petrolia earthquake and reported by Jayko and others (1992) 
and Stein and others (1993). 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Locations of waste water facilities are shown on Maps W-1 and W-2. 

MAP NO . WASTE WATER FACILITIES 
WW1 Fortuna Treatment Plant 

MMI IX 

High liquefaction potential 

Closed for more than 3 days 

Damage to the plant and loss of water and power will result in discharge of untreated 

sewage into the Eel River. 

WW2 Ferndale Treatment Plant 

MMI IX 

High liquefaction potential 
Closed for more than 3 days 

Damage to the plant and loss of water and power will result in discharge of untreated 
sewage into the Salt River. 

WW3 Elk River Sewage Treatment Plant, Eureka 

MMI IX 

High liquefaction potential 

Closed for an extended period 



133 



NORTH COAST SCENARIO 

While this facility is newer than the one serving Areata, severe damage can be expected 
resulting in discharge of sewage into Humboldt Bay. 

WW4 Areata Waste Water Treatment Facility 

MMI IX 

High liquefaction potential 

Closed for an extended period 

Severe damage can be expected to this facility on the north shore of Areata Bay 

resulting in discharge of sewage into the bay. 

WW5 Fisher Treatment Plant, McKinleyville 

MMI VIII + 

Closed for 3 days 

Damage will result in discharging sewage to Mad River slough and the ocean. 

WW6 Water Pollution Control Facility, Crescent City 

MMI VIII + 

In the tsunami inundation zone 

Closed for an extended period 

The combination of strong ground shaking and tsunami damage will destroy 

this facility. Of special concern are unanchored chlorine bottles which could 

break and spill. This would create a dangerous chlorine gas cloud, requiring 

the evacuation of the nearby area. 



134 



NORTH COAST SCENARIO 

PETROLEUM PRODUCTS 
General Characteristics 

Petroleum products are delivered by barge and truck to local distributors' facilities in the two-county 
planning area. The principal distributors' facilities are along the eastern Humboldt Bay shoreline and 
on the southeastern edge of Crescent City. 

Representative storage tank terminals in Humboldt and Del Norte counties were visited in the field 
and assessed for earthquake damage potential. 

Historical Oil Field Operations 

Deposits of oil and natural gas have been recognized in the Bear River-Mattole-Briceland area of 
southwestern Humboldt County by settlers since 1 860. Indications of petroleum such as seeps, led 
to the first California oil well being drilled about 3.5 miles (6 km) northeast of Petrolia in 1865. 
Since then, about 1 85 oil and gas wells have been drilled in southwestern Humboldt County, 
between Eureka and Garberville, and two near Crescent City in Del Norte County. However, only 
small quantities of oil were discovered and only one commercial oil field and two commercial gas 
fields were developed. The Petrolia oil field is about 3 miles (5 km) north of Petrolia. The field 
consists of two wells that produced oil from 1953 until the field was abandoned in 1971 . There are 
currently no active petroleum producing fields in the planning area. 

Seismic Considerations 

In general, earthquake damage to petroleum facilities falls in two categories: 

1 . Damage may occur to transportation or dock facilities for incoming petroleum products. 

2. Tank farms and distribution facilities may: 

a) Suffer direct damage such as broken piping, ruptured storage tanks, and damage 
to buildings and pumping equipment 

b) Suffer serious secondary damage from post-earthquake fire 

c) Become nonfunctional due to loss of water or electric power 

d) Become inaccessible due to liquefaction and ground failures where such facilities 
are on soft ground. 

The few remaining active petroleum storage tank farms along the shoreline of Humboldt Bay are in 
areas of soft soil, in MMI IX zones, and are highly subject to liquefaction. Some are also along the 
bay margins which are within the postulated tsunami run-up area (e.g., Buhne Point). 

There have been isolated instances of fires resulting from damaged storage tanks such as those at 
petroleum tank farms along the Seward waterfront following the 1 964 Alaska earthquake (NAS, 

135 



NORTH COAST SCENARIO 



1973). One particular account of tank damage after the Great Alaska earthquake details that: 

"In Seward, Alaska, burning oil on the surface of surging water in Resurrection Bay (due 
to tsunami-ruptured tanks after the 1 964 earthquake) was spectacular" (Steinbrugge, 
1982). 



Damage to storage tanks come from sidewall buckling, bottom plate separation from sidewalls, and 
from the sloshing of liquids. Sloshing often damages or destroys fixed or floating tank tops. Rigidly 
connected piping also often breaks when the tank rocks because the piping does not possess 
sufficient flexibility. While spillage of oil from such damage may be spectacular, it has not been 
serious when contained within dikes and kept free of ignition sources. 

There were many reports of tank damage following the 1989 Loma Prieta earthquake (M7). 
Damage was primarily related to uplift of unanchored tank walls and typically occurred at soft soil 
sites (Tuttle and others, 1990). Major leaks occurred in several tanks, but the spillage remained 
within containment dikes. No fires occurred (EERI, 1990). 

During the 1994 Northridge earthquake (M6.7) two accounts of damage to storage tanks were 

recorded as follows: 

"Of approximately 12 oil storage tanks (e.g., at the Aliso Canyon Gas Storage Facility), 
six were damaged. One tank collapsed and another at the same location sustained a 
split seam. Damage at other oil storage tanks was relatively minor and consisted of 
buckling and warping of seams" (O'Rourke, 1994). 

"At an oil pumping site, there was severe damage to oil tanks. Contents escaped but 
were retained within containment dikes. ...Contents were lost at an 800,000 gallon 
water tank near Valencia after the piping ruptured. The tank also suffered roof damage 
and elephant's foot buckling at its base. ...An anchored waste oil tank (approx. 10,000 
gal.) pulled its anchors and shifted, breaking the discharge pipe and emptying its 
contents. A 250,000 gal. unanchored fire-water tank experienced an 'elephant's foot' 
failure around the entire base circumference. The tank discharge pipe was damaged, 
apparently by tank uplift, and the tank lost its contents" (EERI, 1994). 

Planning Considerations 

During the 1 989 Loma Prieta event numerous nearly full, unanchored tanks on soft ground, with 
height to width ratios of greater than 0.5 were damaged. Three tanks leaked, but the material was 
trapped by containment dikes. No fires occurred. Most facilities were back in operation within 6 
days after the earthquake (EERI, 1990, pp. 218-238). 

Facilities used for the manufacture, processing, and storage of various petrochemicals warrant 
special attention to reduce the risk of post-earthquake fire and the release of toxic substances. For 
example, unanchored tanks at soft soil sites at tank terminals are especially susceptible to damage 

136 



NORTH COAST SCENARIO 

and leaks. Leaks may also result from breaks in rigidly connected piping. Because of the possibility 
of post-earthquake fire and environmental damage, tanks should be given detailed seismic 
evaluations. 

The low earthen embankments used as retention dikes around fuel and oil storage tanks, 
evaporation ponds and waste containments are subject to failure from earthquake shaking and 
deformation. Also, if valves in the dikes are left open during the rainy season, fuel from damaged 
tanks will escape. The locations of these types of structures, their vulnerability, and the 
consequences of failure need to be examined as part of any emergency planning program. This is 
especially true in the Humboldt Bay area where such tanks exist on the Bay's margins, and also may 
be subject to tsunami damage as was the case in Alaska. 

Ground failures resulting from liquefaction can result in abrupt differential ground movements that 
cause pipe ruptures. Pipe connections at terminal facilities are also vulnerable due to the differing 
responses of buried pipes and rigid structures. 

Shut-off valves are frequently installed in many facilities and on pipelines. These function 
automatically when the line pressure drops below a particular threshold, such as would occur in the 
case of a pipe rupture. Some of these valves depend on electrical power, however, and will not 
function if power is lost. Should a petroleum pipe rupture during the dry season, a post-earthquake 
fire could be a serious problem. This threat is also present during the rainy season should escaping 
fluids be ignited as storm waters wash them into sewers. 

All of the petroleum product storage and distribution facilities in the area should be examined in 
detail relative to their vulnerability to ground failure. The adequacy and locations of automatic 
shut-off valves should also be examined for post-earthquake functioning. Locations for temporary 
storage of emergency fuel supplies, including those for aviation fuels, should be predetermined and 
emergency procedures established to ensure that these supplies will be available when needed. 

Planning Scenario 

Damage can be expected, such as ruptured tanks, buckled steel racks and pumping platforms, 
stretched anchor bolts, stretched or buckled bracing in support structures, broken and cracked 
piping, and piping shifted off its supports. Steel tanks that are not anchored to their foundations 
will rock or shift, rupturing some tanks and breaking attached rigid piping. For planning purposes, 
we assume at least 10 percent of the flat bottom tanks in the planning area will rupture and leak. 
Further damage is unlikely but could result from the tsunami generated by this scenario earthquake. 



137 



NORTH COAST SCENARIO 

Most tsunami damage will occur along the Samoa Peninsula west of Humboldt Bay and the Buhne 
Point area near Eureka. In Crescent City, expected tsunami inundation reaches Eighth Street, and 
thus will affect petroleum tanks there. 

Given the north coast's dependence on long haul petroleum product supply, and the vulnerability of 
marine facilities, Highway 101, and the local tank facilities, there will likely be a gasoline and diesel 
shortage in the planning area. This could necessitate the activation of energy shortage contingency 
plans at the county and state levels. 

Damage Assessments 

Damage assessments have been postulated for certain major facilities as set forth below. The 
statements regarding the performance of facilities are hypothetical and intended for planning 
purposes only. They are not to be construed as site-specific engineering evaluations. Outage and 
repair times assume that materials, equipment, and human resources are available concurrently for 
each damage locality. They will probably not be available concurrently, and outages could be much 
longer than estimated here. Locations of petroleum products storage and facilities are shown on 
Maps EGP-1 and EGP-2. 

MAP NO . PETROLEUM FACILITIES 

PI Chevron Tank Farm, southwest of Eureka 

MMI IX 

High liquefaction potential 

Bordering tsunami run-up zone 

Closed for more than 3 days 

Chevron Oil has tank farms at the south end of Eureka adjacent to Bayshore Mall. Due 

to strong ground motion and liquefaction, pipe breaks will occur in the facility and in the 

tank manifold system. Tank ruptures will occur from the sloshing of liquids, leading to 

spills and the possibility of fire. 

P2 Unocal Tank Farm, west of Eureka 

MMI IX 

High liquefaction potential 
Bordering tsunami run-up zone 
Closed for more than 3 days 
Buckling and leakage of contents will result in contamination and possible fires. 



138 



NORTH COAST SCENARIO 

P3 Tank Farms, southeast of Crescent City 

MMI VIII + to IX 

High liquefaction potential 

Tsunami inundation zone 

Closed for an extended period 

Both tank farms on Highway 101 will be severely damaged by the tsunami, resulting in 

spills and possibly fire. 

P4 Chevron Tank Farms, in Crescent City 

MMI VIII -h 

Tsunami inundation zone 

Closed for an extended period 

The local Chevron Oil Company distributor has two facilities near downtown Crescent 

City. One at Battery and A streets has five large vertical tanks, and the other at 2nd 

and D streets has five smaller ones. Both facilities will be severely damaged by the 

tsunami, resulting in spills and possibly fire. 



139 



NORTH COAST SCENARIO 



GLOSSARY 



ALLUVIUM 
BEDROCK 
DEFORMATION 
EARTHQUAKE 

FAULT 
FAULT LINE 



Surficial sediments consisting of poorly consolidated gravels, 
sands, silts, and clays deposited by flowing water. 

A general term for coherent, usually solid rock, that underlies 
soil or other unconsolidated surficial material. 

A general term for the processes of folding, faulting, shearing, 
compression, or extension of rocks. 

Vibratory motion propagating within the earth or along its 
surface caused by the abrupt release of strain from elastically 
deformed rock by displacement along a fault. 

A fracture (rupture) or a zone of fractures along which there has 
been displacement of adjacent earth material. 

A scarp that has been produced by differential erosion along an 
old fault line. 



GROUND FAILURE 



GROUND RUPTURE 



ISOSEISMAL AREA 



INTENSITY 



LIFELINES 



LIQUEFACTION 



MAGNITUDE 



MODIFIED MERCALLI 
INTENSITY SCALE 

REINFORCED MASONRY 



Permanent ground displacement produced by fault rupture, 
differential settlement, liquefaction, or slope failure. 

Displacement of the earth's surface as a result of fault 
movement associated with an earthquake. 

An area composed of points of equal earthquake intensity on 
the earth's surface. 

A measure of the effects of an earthquake at a particular place. 
Intensity depends on the earthquake magnitude, distance from 
epicenter, and on the local geology. 

Facilities such as highways, bridges, tunnels, major airports, 
electrical power lines, fuel pipelines, communication lines, water 
supply lines, marine terminals and railroads. 

The transitory transformation of sandy water- saturated 
alluvium with properties of a solid into a state possessing 
properties of a liquid as a result of earthquake shaking. 

A measure of the size of an earthquake, as determined by 
measurements from seismographic records. 

Refer to Appendix A. 



Masonry construction with steel reinforcement. 



140 



NORTH COAST SCENARIO 



GLOSSARY (cont.) 



ROSSI-FOREL Refer to Appendix A. 

INTENSITY SCALE 

WATER TABLE The upper surface of ground water saturation of pores and 

fractures in rock or surficial earth materials. 



141 



NORTH COAST SCENARIO 



REFERENCES 



Aalto, K.R., 1981, Unpublished geologic map of the Crescent City 7.5-minute quadrangle: California 
Department of Conservation, Division of Mines and Geology Regional Map File, scale 1 :62,500. 

Alexander, D. and Formichi, R., 1993, Tectonic causes of landslides: Earth Surface Processes and 
Landforms, v. 18, p. 311-338. 

Algermissen, S.T., 1978, Estimation of earthquake losses to buildings (except single family dwellings): U.S. 
Geological Survey Open-File Report 78-441, p. 12-27. 

Algermissen, S.T., Rinehart, W.A., Sherburne, R.W., and Dillinger, W.H., Jr., 1969, Preshocks and 

aftershocks of the Prince William Sound Earthquake of March 28, 1964, in Leipold, L.E., and Wood, 
F.J., eds., The Prince William Sound, Alaska earthquake of 1 964 and aftershocks: U.S. Department of 
Commerce, U.S. Government Printing Office, Washington, D.C. 

Algermissen, S.T. and Steinbrugge, K.V., 1978, Estimation of Earthquake Losses to Buildings (except single 
family dwellings): U.S. Geological Survey Open-File Report 78-441. 

Applied Technology Council, 1985, ATC-13: Earthquake damage evaluation data for California: Federal 
Emergency Management Agency Contract No. EMW-C-0912, 492 p. 

Atwater, B.F., 1986, Holocene subduction earthquakes in coastal Washington labs. I: EOS, Transactions of 
the American Geophysical Union, v. 67, no. 44, p. 906. 

Atwater, B.F., 1987, Evidence for great Holocene earthquakes along the outer coast of Washington state: 
Science, v. 236, p. 942-944. 

Atwater, B.F., 1 992, Geologic evidence for earthquakes during the past 2000 years along the Copalis River, 
southern coastal Washington: Journal of Geophysical Research, v. 97, p. 1901-1919. 

Atwater, B.F. and Grant, W.C., 1 986, Holocene subduction earthquakes in coastal Washington: EOS, 
Transactions of the American Geophysical Union, 67(44)906. 

Back, William, 1957, Geology and ground-water features of the Smith River plain, Del Norte County, 
California: U.S. Geological Survey Water-Supply Paper 1254, 76 p. 

Barosh, P.J., 1 969, Use of seismic intensity data to predict the effects of earthquakes and underground 
nuclear explosions in various geologic settings: U.S. Geological Survey Bulletin 1279, 93 p. 

Beck, S.L. and Nishenko, S.P., 1990, Variations in the mode of great earthquake rupture along the central 
Peru Subduction Zone: Geophysical Research Letters, v. 17, p. 1969-1972. 

Bernard, E., Mader, C, Curtis, G., and Satake, K., 1994, Tsunami inundation model study of Eureka and 
Crescent City, California: National Oceanic and Atmospheric Administration (NOAA) Technical 
Memorandum ERL PMEL, contrib. no. 1536, 80 p., 2 maps. 

Boore, D.M., Joyner, W.B., and Fumal, T.E., 1993, Estimation of response spectra and peak accelerations 
from western North American earthquakes: An interim report, U.S. Geological Survey Open-File Report 
93-509, 72 pp. 

Borchardt, Glenn, 1991, Preparation and use of earthquake planning scenarios: CALIFORNIA GEOLOGY, 
v. 44, p. 195-203. 

Burke, R.M. and Carver, G.A., eds., 1992, A look at the southern end of the Cascadia Subduction Zone and 
the Mendocino Triple Junction: Pacific Cell, Friends of the Pleistocene Guidebook for the field trip to 
Northern Coastal California, June 5-7, 1992, 265 p. 



142 



NORTH COAST SCENARIO 



Byrne, D.E., Davis, D.M., and Sykes, L.R., 1988, Loci and maximum size of thrust earthquakes and the 
mechanics of the shallow region of subduction zones: Tectonics, v. 7, p. 833-837. 

California Department of Education, 1992, California public school directory: California Department of 
Education, Sacramento. 

California Department of Education, 1993, California public school directory: California Department of 
Education, Sacramento, California. 

California Department of Finance, 1 994, Population Estimates, January 1 , 1 994: California Department of 
Finance Report 94-E. 

California Department of Health Services, 1992, Health Facilities Directory, July 1992: California Department 
of Health Services, Division of Licensing and Certification, California. 

California Seismic Safety Commission, 1992, The right to know: Disclosure of seismic hazards in buildings: 
California Seismic Safety Commission Report SSC 92-03, 49 p. 

Carver, G.A., 1993, personal communication. 

Carver, G.A. and Burke, R.M., 1987a, Late Holocene paleoseismicity of the southern end of the Cascadia 

Subduction Zone (abs.]: EOS, Transactions of the American Geophysical Union, v. 68, no. 44, p. 1240. 

Carver, G.A. and Burke, R.M., 1987b, Late Pleistocene and Holocene paleoseismicity of Little Salmon and 
Mad River thrust systems, N.W. California-implications to the seismic potential of the Cascadia 
Subduction Zone (abs.]: Geological Society of America Abstracts with Programs, Cordilleran Section, 
p. 614. 

Carver, G.A. and Burke, R.M., 1989, Trenching investigations of northwestern California faults, Humboldt 
Bay region: Final technical report for the U.S. Geological Survey National Earthquake Hazards Reduction 
Program, 53 p. 

Carver, G.A. and Burke, R.M., 1992, Late Cenozoic deformation on the Cascadia subduction zone in the 

region of the Mendocino Triple Junction, in Burke, R.M., and Carver, G.A., eds., A look at the southern 
end of the Cascadia Subduction Zone and the Mendocino Triple Junction: Pacific Cell, Friends of the 
Pleistocene Guidebook for the field trip to Northern Coastal California, p. 31-63. 

Castillo, D.A. and Ellsworth, W.L., 1993, Seismotectonics of the San Andreas fault system between Point 
Arena and Cape Mendocino in northern California: Implications for the development and evolution of a 
young transform: Journal of Geophysical Research, v. 98, p. 6543-6560. 

Chakos, A. and Nathe, S.K., 1992, Unacceptable risk: Earthquake hazard reduction in one East Bay school 
district: California State University, Hayward, California. 

Clarke, S.H., Jr., 1 992, Tectonic framework of the northern California continental margin: Earthquakes and 
Volcanoes, v. 23, p. 94-100. 

Clarke, S.H., Jr., and Carver, G.A., 1992, Late Holocene tectonics and paleoseismicity of the southern 
Cascadia Subduction Zone, northwestern California: Science, v. 255, p. 188-192. 

Cockerham, R.S., 1984, Evidence for a 180-km-long subducted slab beneath northern California: Bulletin of 
the Seismological Society of America, v. 74, p. 569-576. 

Conlin, K., 1991, Tsunami '64: Tidal Wave Rocks Crescent City: The Humboldt Historian, January-February 
1991, v. 39, no. 1. 

Crouse, C.B., 1991, Ground-motion attenuation equations for earthquakes on the Cascadia Subduction Zone: 
Earthquake Spectra, v. 7, p. 201-236. 



143 



NORTH COAST SCENARIO 



CUSEC, 1994, Northridge, California Earthquake: Implications for the Central U.S.: The Central United States 
Earthquake Consortium, Memphis, Tennessee, Spring 1994, v. 2, no. 1. 

Darienzo, M.E. and Peterson, CD., 1990, Episodic tectonic subsidence of late Holocene salt marshes, 
northern Oregon coast, central Cascadia margin, USA: Tectonics, v. 9, p. 1-22. 

Davenport, C.W., 1982, Geology and geomorphic features related to landsliding, Crescent City 7.5-minute 
quadrangle, Del Norte County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 81-21 SF, scale 1:24,000. 

Davenport, C.W., 1983, Geology and geomorphic features related to landsliding, Hiouchi 7.5-minute 

quadrangle, Del Norte County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 83-4 SF, scale 1:24,000. 

Davenport, C.W., 1983, Geology and geomorphic features related to landsliding in part of the High Divide 
quadrangle, Del Norte County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 83-18 SF, scale 1:24,000. 

Davenport, C.W., 1983, Geology and geomorphic features related to landsliding, Smith River 7.5-minute 

quadrangle, Del Norte County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 83-19, scale 1:24,000. 

Davenport, C.W., 1984, Geology and geomorphic features related to landsliding, Childs Hill 7.5-minute 

quadrangle, Del Norte County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 84-7, scale 1:24,000. 

Davenport, C.W., 1984, Geology and geomorphic features related to landsliding, Requa 7.5-minute 

quadrangle, Del Norte County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 84-8, scale 1:24,000. 

Davis, J.F., Bennett, J.H., Borchardt, G.A., Kahle, J.E., Rice, S.J., and Silva, M.A., 1982a, Earthquake 
planning scenario for a magnitude 8.3 earthquake on the San Andreas fault in southern California: 
California Department of Conservation, Division of Mines and Geology Special Publication 60, 1 28 p. 

Davis, J.F., Bennett, J.H., Borchardt, G.A., Kahle, J.E., Rice, S.J., and Silva, M.A., 1982b, Earthquake 
planning scenario for a magnitude 8.3 earthquake on the San Andreas fault in the San Francisco Bay 
area: California Department of Conservation, Division of Mines and Geology Special Publication 61, 
160 p. 

Davis, J.F., Bennett, J.H., Borchardt, Glenn, Kahle, J.E., Rice, S.J., and Silva, M.A., 1982, Slides and script 
for earthquake planning scenario for a magnitude 8.3 earthquake on the San Andreas fault in the San 
Francisco Bay area, California (Based upon Special Publication 61): California Department of 
Conservation, Division of Mines and Geology Open-File Report 82-23 SF (includes 10 slides), 19 p. 

Davis, J.F., Bennett, J.H., Borchardt, G.A., Rice, S.J., and Silva, M.A., 1982, Damage scenario for a 
magnitude 8.3+ earthquake on the San Andreas fault in the San Francisco Bay Area, in Hart, E.W., 
Hirschfeld, S.E., and Schulz, S.S., eds., Proceedings of the Conference on Earthquake Hazards in the 
Eastern San Francisco Bay Area: California Department of Conservation, Division of Mines and Geology 
Special Publication 62, p. 329-344. 

Davis, J.F., Gray, C.H., Jr., and Kahle, J.E., 1985, Earthquake planning scenarios for magnitude 8.3 
earthquakes on the San Andreas fault near Los Angeles and near San Francisco, California: 
CALIFORNIA GEOLOGY, v. 38, no. 4, p. 87-92. 

Dengler, L., Carver, G., and McPherson, R., 1992, Sources of north coast seismicity: CALIFORNIA 
GEOLOGY, v. 45, p. 40-53. 

Dengler, L. and McPherson, R., 1993, The 17 August 1991 Honeydew earthquake, north coast California: A 
case for revising the Modified Mercalli Scale in sparsely populated areas: Bulletin of the Seismological 
Society of America, v. 83, p. 1081-1095. 

144 



NORTH COAST SCENARIO 



Dengler, L. and Moley, K., 1992, On shaky ground: Living with earthquakes on the north coast: Areata, 
California: Humboldt State University, scale 1:250,000. 

Dengler, L, Moley, K., McPherson, R., Pasyanos, M., Dewey, J. and Murray, M., 1995 (in press), The 
September 1, 1994 Mendocino fault earthquake: CALIFORNIA GEOLOGY, v. 4, no. 2. 

Dunklin, Thomas, 1992, Local effects of 1991-1992 earthquake sequence, in Burke, R.M. and Carver, G.A., 
eds., A look at the southern end of the Cascadia Subduction Zone and the Mendocino Triple Junction: 
Pacific Cell, Friends of the Pleistocene Guidebook for the field trip to Northern Coastal California, June 
5-7, 1992, p. 197-198. 

Dwyer, M.J. and Borchardt G.A., 1994, Paleoseismicity and liquefaction potential of a Sangamon marine 
terrace near the San Andreas fault, Sonoma County, California (abs): in Prentice, C.S., Schwartz, D.P., 
and Yeats, R.S., eds., Proceedings of the Workshop on Paleoseismology: U.S. Geological Survey 
Open-File Report 94-568, p. 59-61. 

EERI, 1980, Reconnaissance Report, 1979 Imperial County, California Earthquake. 

EERI, 1990, Loma Prieta Earthquake Reconnaissance Report: Earthquake Spectra, Earthquake Engineering 
Research Institute, May 1990, Supplement to v. 6, p. 448. 

EERI, 1992b, Landers and Big Bear earthquakes of June 28 & 29, 1992: EERI Newsletter, Earthquake 
Engineering Research Institute, August 1992, v. 26, no. 8, p. 1. 

EERI, 1992a, Cape Mendocino Earthquake, April 25, 1992: EERI Newsletter, Earthquake Engineering 
Research Institute, July 1992, v. 26, no. 7, p. 1-4. 

EERI, 1993, Reconnaissance report from Hokkaido-nansei-oki: EERI Newsletter, Earthquake Engineering 
Research Institute, August, 1993. 

EERI, 1994, Northridge Earthquake January 17, 1994, Preliminary Reconnaissance Report: Earthquake 
Engineering Research Institute, March 1994, 104 p. 

Evenson, R.E., 1959, Geology and ground-water features of the Eureka area, Humboldt County, California: 
U.S. Geological Survey Water-Supply Paper 1470, 80 p. 

Evernden, J.F., 1993, written communication. 

Evernden, J.F., Kohler, W.M., and Clow, G.D., 1981, Seismic intensities of earthquakes of conterminous 
United States-Their prediction and interpretation: U. S. Geological Survey Professional Paper 1223, 
56 p. 

Evernden, J.F. and Thomson, J.M., 1985, Predicting seismic intensities, in Ziony, J. I., ed., Evaluating 
earthquake hazards in the Los Angeles region: An earth science perspective: U.S. Geological Survey 
Professional Paper 1360, p. 151-202. 

Figueroa, J., 1973, Macrosismo del 30 de Enero de 1973: Ingenieria Sismica, Universidad National Atonoma 
de Mexico, 1-24, septiembre-diciembre. 

Fumal, T.E. and Tinsley, J.C., 1985, Mapping shear-wave velocities of near-surface geologic materials in 
Ziony, J. I., ed., Evaluating earthquake hazards in the Los Angeles region: An earth science perspective: 
U.S. Geological Survey Professional Paper 1360, p. 127-149. 

Gonzalez, F.J. and Bernard, E.N., 1992, The Cape Mendocino tsunami, in Special Issue: The Cape 
Mendocino earthquakes of April 25-26, 1992: Earthquakes & Volcanos, v. 23, p. 135-138. 

Grant, W.C. and Minor, R., 1991, Paleoseismic evidence and prehistoric occupation associated with late 
Holocene sudden submergence, northern Oregon coast [absl: EOS, Transactions of the American 
Geophysical Union, v. 72, p. 313. 



145 



NORTH COAST SCENARIO 



Greene, H.G. and Kennedy, M.P., eds., 1989, Geology of the northern California continental margin-Area 7 
of 7: California Department of Conservation, Division of Mines and Geology Continental Margin 
Geologic Map Series, scale 1:250,000. 

Griffin, W.H., 1984, Crescent City's Dark Disaster, Crescent City Printing, Inc. 

Hart, E.W., 1 992, Fault-rupture hazard zones in California (revised edition): California Department of 
Conservation, Division of Mines and Geology Special Publication 42, 32 p. 

Heaton, T.H. and Kanamori, H., 1984, Seismic potential associated with subduction in the northwestern 
United States: Bulletin of the Seismological Society of America, v. 74, p. 933-941. 

Heaton, T.H. and Hartzell, S.H., 1986, Source characteristics of hypothetical subduction earthquakes in the 
northwestern United States: Bulletin of the Seismological Society of America, v. 76, p. 675-708. 

Heaton, T.H. and Hartzell, S.H., 1987, Earthquake hazards on the Cascadia Subduction Zone: Science, 
v. 236, p. 162-168. 

Houston, H., 1992, The exception is the rule: Nature, v. 360, p. 111-112. 

Humboldt County Planning Department, 1979, Seismic safety and public safety elements of the Humboldt 
County general plan: Humboldt County Planning Department, Eureka, California, 57 p. 

Jachens, R.C. and Griscom, Andrew, 1983, Three-dimensional geometry of the Gorda plate beneath northern 
California: Journal of Geophysical Research, v. 88, p. 9375-9392. 

Jayko, A.S., Marshall, G.A., and Carver, G.A., 1992, Elevation changes, in Special issue: The Cape 
Mendocino earthquakes of April 25-26, 1992: Earthquakes and Volcanoes, v. 23, p. 139-143. 

Jephcott, D.K. and Hudson, D.E., 1974, School Report - The performance of public school plants during the 
San Fernando earthquake: Center for Research on the Prevention of Natural Disaster, California Institute 
of Technology, Pasadena, California. 

Joyner, W.B. and Boore, D.M., 1988, Measurement, characterization, and prediction of strong ground 
motion: Proceedings of Earthquake Engineering and Soil Dynamics II GT Div/ASCE, Park City, UT, 
June 27-30, p. 43-102. 

Kanamori, H., 1977, The energy release in great earthquakes: Journal of Geophysical Research, v. 82, 
p. 2981-2987. 

Keefer, D.K., 1984, Landslides caused by earthquakes: Geological Society of America, v. 95, p. 406-421. 

Keefer, D.K., 1991, personal communication. 

Kelley, F.R., 1984, Geology and geomorphic features related to landsliding in the Areata North 7.5-minute 
quadrangle, Humboldt County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 84-38, scale 1:24,000. 

Kelley, F.R., 1984, Geology and geomorphic features related to landsliding in the Areata South 7.5-minute 
quadrangle, Humboldt County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 84-39, scale 1 :24,000. 

Kilbourne, R.T., 1982, Geology and geomorphic features related to landsliding in the Glenblair NW 

7.5-minute quadrangle, Humboldt County, California: California Department of Conservation, Division of 
Mines and Geology Open-File Report 82-25 SF, scale 1:24,000. 

Kilbourne, R.T., 1985, Geology and geomorphic features related to landsliding in the Fortuna 7.5-minute 

quadrangle, Humboldt County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 85-1, scale 1:24,000. 



146 



NORTH COAST SCENARIO 



Kilbourne, R.T., 1985, Geology and geomorphic features related to landsliding in the Hydesville 7.5-minute 
quadrangle, Humboldt County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 85-2, scale 1:24,000. 

Kilbourne, R.T., 1985, Geology and geomorphic features related to landsliding in the McWhinney Creek 

7.5-minute quadrangle, Humboldt County, California: California Department of Conservation, Division of 
Mines and Geology Open-File Report 85-3 SF, scale 1:24,000. 

Kilbourne, R.T., 1985, Geology and geomorphic features related to landsliding in the Korbel 7.5-minute 

quadrangle, Humboldt County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 85-5 , scale 1 :24,000. 

Kilbourne, R.T., 1985, Geology and geomorphic features related to landsliding in the Blue Lake 7.5-minute 
quadrangle, Humboldt County, California: California Department of Conservation, Division of Mines and 
Geology Open-File Report 85-6, scale 1:24,000. 

Kilbourne, R.T. and Morrison, S.D., 1985, Geology and geomorphic features related to landsliding in the 
Fields Landing 7.5-minute quadrangle, Humboldt County, California: California Department of 
Conservation, Division of Mines and Geology Open-File Report 85-4, scale 1 :24,000. 

Kilbourne, R.T. and Mualchin, Lalliana, 1981, Geology for planning: Crescent City and Sister Rocks 

7.5-minute quadrangles, Del Norte County, California: California Department of Conservation, Division 
of Mines and Geology Open-File Report 81-1, 48 p. 

Kilbourne, R.T., Mualchin, Lalliana, and Saucedo, G.J., 1980, Geology for Planning: Eureka and Fields 

Landing 7.5 quadrangles, Humboldt County, California: California Department of Conservation, Division 
of Mines and Geology Open-File Report 80-9 SF, 49 p. 

Kilbourne, R.T. and Saucedo, G.J., 1981, Gorda Basin earthquake, northwestern California: CALIFORNIA 
GEOLOGY, v. 34, no. 3, p. 53-57. 

Lagorio, H.J., 1990, Earthquakes: An architect's guide to non-structural seismic hazards: New York: Wiley, 
312 p. 

Lagorio, H.J., 1 994, Importance of Lifeline Systems in Rapid Urban Post-Earthquake Recovery Strategies, 
Proceedings of Second China-Japan-U.S.A. Trilateral Symposium on Lifeline Earthquake Engineering: 
Ministry of Construction (China), Kobe University (Japan), and NSF (U.S.A.). 

Lagorio, H.J., Friedman, H., and Wong, K., 1986, Issues for the seismic strengthening of existing buildings - 
A practical guide for architects: Center for Environmental Design Research (CEDR), University of 
California, Berkeley, California. 

Lajoie, J.R., Kennedy, G.L., Mathieson, S.A., Sarna-Wojcicki, A.M., Morrison, S.A., and Tobish, M.K., 1983, 
Emergent Holocene marine terraces at Cape Mendocino and Ventura, California, U.S.A.: Proc. 
International Symposium on Development of Holocene Shorelines, Tokyo, Japan. 

Lander, J.F. and Lockridge, P.A., 1989, United States Tsunamis: 1960-1988: Department of Commerce, 
National Oceanic and Atmospheric Administration (NOAA), Publication 41-2. 

Lander, J.F., Lockridge, P.A., and Kozuch, M.J., 1993, Tsunamis Affecting the West Coast of the United 
States, 1806-1992: Department of Commerce, National Oceanic and Atmospheric Administration 
(NOAA), Documentation No. 29. 

LNG Task Force, 1 980, Recommendations for an earthquake hazards reduction program: Report prepared for 
the California Seismic Safety Commission by the California Public Utilities Commission, San Francisco, 
California. 

Louderback, G.D., Benioff, H., Macelwane, J.B., 1955, Eureka, California, December 21, 1954: 
Seismological Notes, Bulletin of the Seismological Society of America. 



147 



NORTH COAST SCENARIO 



Lund, L.V., 1994, Lifeline Performance in the Landers and Big Bear (California) Earthquakes of 28 June 
1992: Bulletin of the Seismological Society of America, June 1994, v. 84, no. 3. 

Manson, M.W., Keefer, D.K., and McKittrick, M.A., 1991, Landslides and other geologic features in the 
Santa Cruz Mountains, California, resulting from the Loma Prieta earthquake of October 17, 1989: 
California Department of Conservation, Division of Mines and Geology Open-File Report 91-5, 45 p. 

Maxson, JJ-L, 1933, Economic geology of portions of Del Norte and Siskiyou counties, northwesternmost 
California: California Journal of Mines and Geology, v. 29, p. 123-160. 

McCulloch, D.S. and Bonilla, M.G., 1970, Effects of the earthquake of March 27, 1964, on the Alaska 
Railroad: U.S. Geological Survey Professional Paper 545-D, 161 p. 

McLaughlin, R.J., 1993, Written communication concerning the geology of the Mendocino and Eureka area: 
U.S. Geological Survey, v. 2 sheets, scale 1:100,000. 

McMillan, J.R. and Gibson, L.R., 1987, Smith River plain ground water study: California Department of 
Water Resources Report, 1 38 p. 

McNutt, S.R., 1990, Summary of damage and losses caused by the Loma Prieta earthquake, in McNutt, 
S.R., and Sydnor, R.H., eds., The Loma Prieta (Santa Cruz Mountains), California, earthquake of 17 
October 1989: California Department of Conservation, Division of Mines and Geology Special 
Publication 104, p. 131-138. 

McPherson, R.C. and Dengler, L.A., 1992, The Honeydew earthquake: August 17, 1991: CALIFORNIA 
GEOLOGY, v. 45, p. 31-39. 

Meehan, J.F., 1983, Performance of the public school buildings to the 1983 Coalinga, California, earthquake: 
in Bennett, J.H., and Sherburne, R.W., eds.. The 1983 Coalinga, California Earthquakes: California 
Department of Conservation, Division of Mines and Geology Special Publication 66, p. 37-54. 

Meehan, J.F., 1990, Performance of Public Schools in the Loma Prieta Earthquake of October 17, 1989: 
Office of the State Architect, Sacramento, California. 

NAS, 1973, The Great Alaska Earthquake of 1964: National Academy of Science, Engineering Volume, 
Washington, DC. 

NISEE, 1992, National clearinghouse for Loma Prieta earthquake information catalog, October 1992: The 
National Information Service for Earthquake Engineering, Earthquake Engineering Research Center 
(EERC), University of California at Berkeley, and Earthquake Engineering Library, California Institute of 
Technology (CALTECH), Pasadena, California. 

Nishimura, C.E., Wilson, D.S., and Hey, R.N., 1984, Pole of rotation analysis of present-day Juan de Fuca 
plate motion: Journal of Geophysical Research, v. 89, p. 10,283-10,290. 

NOAA, 1973, A study of earthquake losses in the Los Angeles, California area, 1973: A report prepared by 
National Oceanic and Atmospheric Administration for the Federal Disaster Assistance Administration, 
Department of Housing and Urban Development, 331 p. 

Oppenheimer, D., Beroza, G., Carver, C, Dengler, L., Eaton, J., Gee, L., Gonzalez, F., Jayko, A., Li, W.H., 
Lisowski, M., Magee, M., Marshall, G., Murray, M., McPherson, R., Romanowicz, B., Satake, K., 
Simpson, R., Somerville, P., Stein, R., and Valentine D., 1993, The Cape Mendocino, California, 
earthquake sequence of April 1992: subduction at the triple junction: Science, v. 261, p. 433-438. 

O'Rourke, T.D. and Palmer, M.C., 1994, Earthquake Performance of Gas Transmission Pipelines During the 
Northridge Earthquake: National Center for Earthquake Engineering Research, NCEER Bulletin, April 
1994, v. 8, no. 2. 

Pacheco, J.F. and Sykes, L.R., 1992, Seismic moment catalog of large, shallow earthquakes, 1900-1989: 
Bulletin of the Seismological Society of America, v. 82, p. 1306-1349. 

148 



NORTH COAST SCENARIO 



Petersen, M.D., Toppozada, T.R., Borchardt, Glenn, and Haydon, Wayne, 1993, Seismic shaking and 
geologic effects in Humboldt and Del Norte counties, northwestern California, from a scenario 
earthquake along the Gorda segment of the Cascadia Subduction Zone: EOS, Transactions of the 
American Geophysical Union, v. 74, no. 43, p. 434. 

Prentice, C.S., Keefer, D.K., and Sims, J.D., 1992, Surface effects of the earthquakes, in Special issue: The 
Cape Mendocino earthquakes of April 25-26, 1992: Earthquakes and Volcanoes, v. 23, p. 127-134. 

Reagor, G. and Brewer, L., 1992, Damage and intensity survey, in Special Issue: The Cape Mendocino 
earthquakes of April 25-26, 1992: Earthquakes and Volcanoes, v. 23, p. 116-123. 

Reichle, M.S. and Kahle, J., 1989, Forecasting seismic intensities for California earthquakes: Sacramento, 
California: California Department of Conservation, Division of Mines and Geology, unpublished report 
available from the authors. 

Reichle, M.S., Kahle, J.E., Atkinson, T.G., and Johnson, E.H., 1990, Planning scenario for a major 

earthquake, San Diego-Tijuana metropolitan area; California Department of Conservation, Division of 
Mines and Geology Special Publication 100, 189 p. 

Reyes, A., Brune, J.N., and Lomnitz, C, 1979, Source mechanism and aftershock study of the Colima, 
Mexico earthquake of January 30, 1973: Bulletin of the Seismological Society of America, v. 69, 
p. 1819-1840. 

Richardson, C.B., 1973, Damage to Utilities, The Great Alaska Earthquake of 1964: National Academy of 
Sciences, Engineering Volume. 

Savage, J.C., Lisowski, M., and Prescott, W.H., 1991, Strain accumulation in western Washington: Journal 
of Geophysical Research, v. 96, p. 14,493-14,507. 

Savage, W. and Matsuda, E., 1994, written communication. 

Scholz, C.H., 1982, Scaling laws for large earthquakes: Consequences for physical models: Bulletin of the 
Seismological Society of America, v. 72, no. 1, p. 1-14. 

Semans, Frank and Zelinski, Ray, 1 980, Final report of the Eureka (Trinidad-offshore) earthquake of 

November 8, 1 980 by the Post Earthquake Investigation Team (PEIT) of Caltrans: California Department 
of Transportation, 1 2 p. 

Shakal, A., Darragh, R., Huang, M., Cao, T., Sherburne, R., Sydnor, R., Malhotra, P., Cramer, C, Wampole, 
J., Fung, P., and Petersen, C, 1992, CSMIP strong-motion records from the Petrolia, California 
earthquakes of April 25-26, 1992: California Department of Conservation, Division of Mines and 
Geology Open-File Report 92-05, 74 p. 

Slemmons, D.B. and Depolo, CM., 1986, Evaluation of active faulting and associated hazards, in Wallace, 
R.E., ed., Active tectonics: National Academy Press (Studies in Geophysics Series), Washington, DC, 
p. 45-62. 

Smith, S.W. and Knapp, J.S., 1980, The northern termination of the San Andreas fault, in Streitz, R. and 
Sherburne, R., eds., Studies of the San Andreas fault zone in northern California: California Department 
of Conservation, Division of Mines and Geology Special Report 140, p. 153-164. 

Smith, S.W., Knapp, J.S., and McPherson, R.C., 1993, Seismicity of the Gorda Plate structure of the 

Continental Margin, and an eastward jump of the Mendocino Triple Junction: Journal of Geophysical 
Research. 

Sparks, N.R., 1936, The Eureka Earthquake of June 6, 1932: Bulletin of the Seismological Society of 
America, v. 26, no. 13. 



149 



NORTH COAST SCENARIO 



Spittler, T.E., Harp, E.L., Keefer, D.K., Wilson, R.C., and Sydnor, R.H., 1990, Landslide features and other 
coseismic fissures triggered by the Loma Prieta earthquake, central Santa Cruz Mountains, California, in 
McNutt, S.R., and Sydnor, R.H., eds., The Loma Prieta, earthquake of 17 October 1989: California 
Department of Conservation, Division of Mines and Geology Special Publication 104, p. 59-66. 

Stein, R.S., Marshal, G.A., and Murray, M.A., 1993, Permanent ground movement associated with the 1992 
M7 Cape Mendocino earthquake, FEMA Damage Survey Report 080632. 

Steinbrugge, K.V., 1982, Earthquakes, volcanoes, and tsunamis: An anatomy of hazards: Skankia America 
Group, New York, 392 p. 

Steinbrugge, K.V., Bennett, J.H., Lagorio, H.J., Davis, J.F., Borchardt, G.A., Toppozada, T.R., Degenkolb, 
H.J., Laverty, G.L., and McCarty, J.E., 1987, Earthquake planning scenario for a magnitude 7.5 
earthquake on the Hayward fault in the San Francisco Bay area: California Department of Conservation, 
Division of Mines and Geology Special Publication 78, 245 p. 

Steinbrugge, K.V., Cloud, W.K., and Scott, N.H., 1970, The Santa Rosa Earthquake of October 1, 1969: 
U.S. Department of Commerce, Rockville, Maryland. 

Steinbrugge, K.V. and Moran, D.F., 1957, An Engineering Study of the Eureka, California Earthquake of 
December 21, 1954: Bulletin of the Seismological Society of America, v. 47, no. 2. 

Stevens, Tom, 1993, personal communication. 

Stover, C.W. and Coffman, J.L., 1993, Seismicity of the United States, 1568-1989 (revised): U.S. 
Geological Survey Professional Paper 1527, 418 p. 

TERA Corporation, 1975, Humboldt Bay seismic network annual report, August 1974 - August 1975: 
unpublished report to the Pacific Gas and Electric Co., San Francisco, California. 

TerraScan, Inc., 1976, Seismic safety and safety element of Del Norte County general plan: Unpublished 
consulting report, Eureka, California, 79 p. 

Toppozada, T.R., Bennett, J.H., Borchardt, G.A., Saul, Richard, Davis, J.F., Johnson, C.B., Lagorio, H.J., 
and Steinbrugge, K.V., 1988, Planning scenario for a major earthquake on the Newport-lnglewood fault 
zone: California Department of Conservation, Division of Mines and Geology Special Publication 99, 
199 p. 

Toppozada, T.R., Borchardt, G.A., Hallstrom, C.L., Johnson, C.B., Ron, Per, and Lagorio, H.J., 1993, 

Planning scenario for a major earthquake on the San Jacinto fault in the San Bernardino area: California 
Department of Conservation, Division of Mines and Geology Special Publication 102, 221 p. 

Toppozada, T.R., Borchardt, G.A., Hallstrom, C.L., Youngs, L.G., Gallagher, R.P., and Lagorio, H.J., 1994, 
Planning scenario for a major earthquake on the Rodgers Creek fault in the northern San Francisco Bay 
area: California Department of Conservation, Division of Mines and Geology Special Publication 112, 
264 p. 

Toppozada, T.R. and Parke, D.L., 1982, Areas damaged by California earthquakes 1900-1949: California 
Department of Conservation, Division of Mines and Geology Open-File Report 82-17 SAC, 65 p. 

Toppozada, T.R., Real, C.R., and Parke, D.L., 1981, Preparation of isoseismal maps and summaries of 

reported effects for pre- 1900 California earthquakes: California Department of Conservation, Division of 
Mines and Geology Open-File Report 81-11 SAC, 182 p. 

Trifunic, M.D. and Brady, A.G., 1975, On the correlation of seismic intensity scales with the peaks of 
recorded strong ground motion: Bulletin of the Seismological Society of America, v. 65, p. 139-162. 

Tuttle, M., Cowie, P., Tinsley, J., Benett, M., and Berrill, J., 1990, Liquefaction and foundation failure of 
Chevron Oil and gasoline tanks at Moss Landing, California: Geophysical Research Letters, v. 17, 
no. 10. 



150 



NORTH COAST SCENARIO 



University of California at Berkeley Seismographic Stations, Bulletin of the seismographic stations of the 
University of California: University of California, Berkeley, California. 

U.S. Department of Transportation, 1982, Vulnerability of transportation systems to earthquakes: U.S. 
Department of Transportation Report No. FHWA/RD-81/128. 

Varner, T. and Varner, L., 1992, Cape Mendocino, California, April 25-26, 1992, EERI Special Earthquake 
Report - June 1992: EERI Newsletter, v. 26, no. 6. 

Wagner, D.L. and Saucedo, G.J., 1987, Geologic map of the Weed quadrangle, California: California 

Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 
4A, scale 1:250,000. 

Wieczorek, G.F., Wilson, R.C., and Harp, E.L., 1985, Map showing slope stability during earthquakes in San 
Mateo County, California: U.S. Geological Survey Miscellaneous Investigation Series Map 1-1257-E, 
scale 1:62,500. 

Wills, C.J., 1 990, Little Salmon and related faults, Humboldt County: California Department of Conservation, 
Division of Mines and Geology Fault Evaluation Report 215, 14 p. 

Wills, C.J. and Manson, M.W., 1990, Liquefaction at Soda Lake: Effects of the Chittenden earthquake 
swarm of April 18, 1990, Santa Cruz County, California: CALIFORNIA GEOLOGY, v. 43, no. 10, 
p. 225-232. 

Wilson, R.C. and Keefer, D.K., 1985, Predicting areal limits of earthquake-induced landsliding, in Ziony, J. I., 
ed., Evaluating earthquake hazards in the Los Angeles region: An earth science perspective: U.S. 
Geological Survey Professional Paper 1360, p. 317-345. 

Wuethrich, B., 1994, It's official: Quake danger in Northwest rivals California's: Science, v. 265, 
p. 1802-1803. 

Wyss, M., 1979, Estimating maximum expectable magnitude of earthquakes from fault dimensions: Geology, 
v. 7, p. 336-340. 

Youd, L., 1994, personal communication. 

Youngs, R.R., Day, S.M., and Stevens, J.L., 1988, Near field ground motions on rock for large subduction 
earthquakes, Earthquake Engineering and Soil Dynamics II, Recent Advances in Ground Motion 
Evaluation ASCE Geotechnical Special Publication 20. 



151 



APPENDIXES 



m 



q 

H 
O 
HI 



SCENARIO MAPS AND DAMAGE ASSESSMENTS 

ARE INTENDED FOR EMERGENCY PLANNING 

PURPOSES ONLY 



THEY ARE BASED ON THE FOLLOWING HYPOTHETICAL 
CHAIN OF EVENTS: 

1 . A PARTICULAR EARTHQUAKE OCCURS 

2. VARIOUS LOCALITIES IN THE PLANNING AREA 
EXPERIENCE A SPECIFIC TYPE OF SHAKING OR 
GROUND FAILURE 

3. CERTAIN CRITICAL FACILITIES UNDERGO DAMAGE AND 
OTHERS DO NOT 

THE CONCLUSIONS REGARDING THE PERFORMANCE OF 
FACILITIES ARE HYPOTHETICAL AND AND NOT TO BE 
CONSTRUED AS SITE-SPECIFIC ENGINEERING EVALUATIONS. 
FOR THE MOST PART, DAMAGE ASSESSMENTS ARE STRONGLY 
INFLUENCED BY THE SEISMIC INTENSITY DISTRIBUTION MAP 
DEVELOPED FOR THIS PARTICULAR SCENARIO EARTHQUAKE. 
THERE IS DISAGREEMENT AMONG INVESTIGATORS AS TO 
THE MOST REALISTIC MODEL FOR PREDICTING SEISMIC 
INTENSITY DISTRIBUTION. NONE HAVE BEEN FULLY TESTED 
AND EACH WOULD YIELD A DIFFERENT EARTHQUAKE 
PLANNING SCENARIO. FACILITIES THAT ARE PARTICULARLY 
SENSITIVE TO EMERGENCY RESPONSE WILL REQUIRE A 
DETAILED GEOTECHNICAL STUDY. 



THE DAMAGE ASSESSMENTS ARE BASED ON THIS SPECIFIC 
SCENARIO. AN EARTHQUAKE OF SIGNIFICANTLY DIFFERENT 
MAGNITUDE ON THIS OR ANY ONE OF MANY OTHER FAULTS 
IN THE PLANNING AREA WILL RESULT IN A MARKEDLY 
DIFFERENT PATTERN OF DAMAGE. 



NORTH COAST SCENARIO 



APPENDIX A 



Modified Mercalli Intensity Scale of Wood and Neumann, 
and its Relation to the Rossi-Forel Scale 
The numbers in parentheses in the left margin and the initials R.F. refer to the Rossi-Forel intensity scale. 

I Not felt— or, except rarely under especially favorable circumstances. 

Under certain conditions, at and outside the boundary of the area in which a great shock is 
felt: 
[I R.F.] sometimes birds, animals, reported uneasy or disturbed; 

sometimes dizziness or nausea experienced; 
sometimes trees, structures, liquids, bodies of water may sway-doors may swing very slowly. 

II Felt indoors by few, especially on upper floors or by sensitive or nervous persons. 

Also, as in grade 1 , but often more noticeably: 
[I to II R.F.] sometimes hanging objects may swing especially when delicately suspended; 

sometimes trees, structures liquids bodies of water may sway, doors may swing 

very slowly; 
sometimes birds animals reported uneasy or disturbed; 
sometimes dizziness or nausea experienced. 

III Felt indoors by several, motion usually rapid vibration. 

Sometimes not recognized to be an earthquake at first. 
[Ill R.F.] Duration estimated in some cases. 

Vibration like that due to passing of light or lightly loaded trucks or heavy trucks some 

distance away. 
Hanging objects may swing slightly. 

Movements may be appreciable on upper levels of tall structures. 
Rocked standing motor cars slightly. 

IV Felt indoors by many, outdoors by few. 

Awakened few, especially light sleepers. 
(IV to V R.F.) Frightened no one unless apprehensive from previous experience. 

Vibration like that due to passing of light or tightly loaded trucks. 
Sensation like heavy body striking building or falling of heavy objects inside. 
Rattling of dishes, windows, doors; glassware, and crockery clink and clash. 
Creaking of walls, frame, especially in the upper range of this grade. 
Hanging objects swung in numerous instances. 
Disturbed liquids in open vessels slightly. 
Rocked standing motor cars noticeably. 

V Felt indoors by practically all, outdoors by many or most: outdoors direction estimated. 

Awakened many or most. 
(V to VI R.F.I Frightened few— slight excitement, a few ran outdoors. 

Buildings trembled throughout. 
Broke dishes, glassware to some extent. 
Cracked windows— in some cases, but not generally. 

Overturned vases, small or unstable objects, in many instances with occasional fall. 
Hanging objects, doors swing generally or considerably. 
Knocked pictures against walls or swung them out of place. 
Opened or closed doors, shutters, abruptly. 
Pendulum clocks stopped, started, or ran fast, or slow. 
Moved small objects, furnishings, the latter to slight extent. 
Spilled liquids in small amounts from well-filled open containers. 
Trees, bushes shaken slightly. 



153 



NORTH COAST SCENARIO 



APPENDIX A (cont.) 



VI Felt by all indoors and outdoors. 

Frightened many, excitement general, some alarm, many ran outdoors. 
[VI to VII R.F.] Awakened all. 

Persons made to move unsteadily. 

Trees, bushes shaken slightly, moderately. 

Liquid set in strong motion. 

Small bells rang— church, chapel, school, etc. 

Damage slight in poorly built buildings. 

Fall of plaster in small amount. 

Cracked plaster somewhat, especially fine cracks; chimneys in some instances. 

Broke dishes, glassware in considerable quantity, also some windows. 

Fall of knick-knacks, books, pictures. 

Overturned furniture in many instances. 

Moved furnishings of moderately heavy kind. 

VII Frightened all-general alarm all ran outdoors. 

Some or many found it difficult to stand. 
[VIII - R.F.] Noticed by persons driving motor cars. 

Trees and bushes shaken moderately to strongly. 

Waves on ponds, lakes, and running water. 

Water turbid from mud stirred up. 

Incaving to some extent of sand or gravel stream banks. 

Rang large church bells, etc. 

Suspended objects made to quiver. 

Damage negligible in buildings of good design and construction, slight to moderate in 
well-built ordinary buildings, considerable in poorly built or badly designed buildings, 

adobe houses, old walls (especially where laid up without mortar), spires, etc. 
Cracked chimneys to considerable extent walls to some extent. 
Fall of plaster in considerable to large amount, also some stucco. 
Broke numerous windows, furniture to some extent. 
Shook down loosened brickwork and tiles. 

Broke weak chimneys at the roof-line (sometimes damaging roofs). 
Fall of cornices from towers and high buildings. 
Dislodged bricks and stones. 

Overturned heavy furniture with damage from breaking. 
Damage considerable to concrete irrigation ditches. 

VIII Fright general-alarm approaches panic. 

Disturbed persons driving motor cars. 
[VIII + to IX - R.F.] Trees shaken strongly-branches, trunks broken off, especially palm trees. 

Ejected sand and mud in small amounts. 
Changes: temporary, permanent; in flow of springs and wells; dry wells renewed flow, 

in temperature of spring and well waters. 
Damage slight in structures (brick) built especially to withstand earthquakes. 
Considerable in ordinary substantial buildings, partial collapse, racked, tumbled down, 

wooden houses in some cases; threw off panel walls in frame structures, broke off 
decayed piling. 
Fall of walls. 
Cracked, broke, solid stone walls seriously. 

Wet ground to some extent, also ground on steep slopes. 
Twisting, fall, of chimneys, columns, monuments, also factory stacks, towers. 
Moved conspicuously, overturned, very heavy furniture. 



154 



NORTH COAST SCENARIO 



APPENDIX A (cont.) 



IX Panic general. 

Cracked ground conspicuously. 
[IX + R.F.] Damage considerable in (masonry) structures built especially to withstand earthquakes: 

threw out of plumb some wood-frame houses built especially to withstand earthquakes; 
great in substantial (masonry) buildings, some collapse in large part; 
or wholly shifted frame buildings off foundations, racked frames; 
serious to reservoirs; underground pipes sometimes broken. 

X Cracked ground, especially when loose and wet, up to widths of several inches; fissures 

up to a yard in width ran parallel to canal and stream banks. 
(X R.F.I Landslides considerable from river banks and sleep coasts. 

Shifted sand and mud horizontally on beaches and flat land. 
Changed level of water in wells. 
Threw water on banks of canals, lakes, rivers, etc. 
Damage serious to dams dikes, embankments. 

Severe to well-built wooden structures and bridges, some destroyed. 

Developed dangerous cracks in excellent brick walls. 

Destroyed most masonry and frame structures, also their foundations. 

Bent railroad rails slightly. 

Tore apart, or crushed endwise, pipe lines buried in earth. 

Open cracks and broad wavy folds in cement pavements and asphalt road surfaces. 

XI Disturbances in ground many and widespread, varying with ground material. 

Broad fissures, earth slumps, and land slips in soft wet ground. 

Ejected water in large amount charged with sand and mud. 

Caused sea-waves (tidal waves) of significant magnitude. 

Damage severe to wood-frame structures, especially near shock centers. 

Great to dams, dikes, embankments, often for long distances. 

Few if any (masonry) structures remained standing. 

Destroyed large well-built bridges by the wrecking of supporting piers or pillars. 

Affected yielding wooden bridges less. 

Bent railroad rails greatly, and thrust them endwise. 

Put pipe lines buried in earth completely out of service. 

XII Damage total-practically all works of construction damaged or greatly destroyed. 

Disturbances in ground great and varied, numerous shearing cracks. 
Landslides, falls of rock of significant character, slumping of river banks, etc., 

numerous and extensive. 
Wrenched loose, tore off large rock masses. 

Fault slips in firm rock with notable horizontal and vertical offset displacements. 
Water channels, surface and underground, disturbed and modified greatly. 
Dammed lakes, produced waterfalls, deflected rivers, etc. 
Waves seen on ground surfaces (actually seen, probably, in some case). 
Distorted lines of sight and level. 
Threw objects upward into the air. 



155 



NORTH COAST SCENARIO 



APPENDIX B 



MAPS OF SEISMIC INTENSITY AND LIFELINES 



SCALE 


MAP NO 


xlOOO 




100 


S-1* 


100 


S-2* 


250 


S-3* 


100 


SHM-1 


100 


SHM-2 


100 


H-1 


100 


H-2 


250 


H-3 


250 


AR 


100 


EGP-1 


100 


EGP-2 


100 


W-1 


100 


W-2 



DESCRIPTION 



Seismic Intensity Distribution 
Seismic Intensity Distribution 
Seismic Intensity Distribution 

Public Schools, Hospitals, and Marine Facilities 
Public Schools, Hospitals, and Marine Facilities 

Highways 
Highways 
Highways 

Airports, Railroads, Electric Power and Natural Gas 

Electric Power, Natural Gas, and Petroleum 
Electric Power, Natural Gas, and Petroleum 

Water Supply and Waste Water 
Water Supply and Waste Water 



'1" indicates Eureka area, "2" indicates Crescent City area, 
'3" indicates Humboldt and Del Norte counties. 



NOTES 

The 100,000-scale intensity maps generally show more detail for the Eureka area (Map S-1) and the 
Crescent City area (Map S-2) than the 250,000-scale Map S-3. 

Narrow coastal strips of MMI IX, such as that northwest of Crescent City on Map S-2, should show 
high liquefaction potential. 

On the 250,000-scale maps S-3, H-3, and AR, the labels for old and new Highway 101 near the 
Humboldt-Del Norte County line should be reversed. 

Map AR should show Kneeland Airport (A5) as open, and Willow Creek Airport (A9) as closed. 



157 




EC 
< 

LU 

o 

CO 
O 



uzo 

I- O N 

^ 111 z 

o * 2 

U?h 

wag 

I- I Q 
DC I- m 



UJ < 
DC o 

a tn 










-" 


o 


2 






O 

h- 
m 






cr 

t- 

V) 

a 






> 

h- 






W 


-. 




z 






I 






o 






UJ 


1 







i J 

; s to 

! 3 W 



/ 



"s °-E ! 



IJoE 



E '5 -° 4 



e £ 5 5 



" E 2 o 
!| | If |1 I I 1| 



11 = 1 ^ I l! S l 1 I I = 



essESBg 

■:- - 



5 
Y 



lb 



ill |l 



i Iff* 1=5 

Isila Hi 









- 

Y;:>* 

- ' : ' 

•Mi -i 




MATCH 



LINE 



-J 

lidiiiiii 

HNS Its 

.- "Slimes 
i MI; S!js5a|;f55 

iiiPlli 
pi! ill 



si 



i 




d^'" 




M A T s 



LINE 



I t- 









z 










rr 










O 










u- 










1 










< 








o 


O 


T 














u-> 


ce 


UJ 


r 


2 

n 


J- 


< 


1- 


o 


N 


■z. 


7* 


z 


HI 


z 


O 

< i 


UJ 

o 


o 
u 

LU 


< 

o 


o 

p 
o 


Zj 

CD 


C5 


1- 
<r 
O 
z 


X 

K 
CC 
< 


D 
m 

ID 

tn 


-1 
< 
(1 


Z 


III 


1- 


< 


z 


o 


< 
l.i.l 


Q 


111 

n 


z 


u 

2 


cc 


o 


in 


_l 


< 

Q 


< 


< 




ssgsaes 
[=■■■; 



i i s 



sssipPIf 



Sill 



I! IIS I 

llfiSll 

liiii gsillsil|i| iif? 

:r' " fsslslsilli :isl 



r 














o 


o 


UJ 

r 










1- 


iii 


in 


DC 


III 


Z 


z 
o 

N 


P 


< 


1- 


o 


Z 
O 


Z 
III 


=1 
o 


UJ 

< 


z 
o 


5 

o 

-I 

CO 
D 
Q. 


o 

(0 




o 

UJ 

H 
CC 

o 

z 


o 

i 

H 

cn 

< 


H 

o 

Q 

m 

=> 

CO 


_l 
< 


Z 


_l 

UJ 

a 


5 

UJ 


< 

D 


UJ 

a 


Z 


z 


IE 

a 


O 


m 


< 


< 




< 




-1 

a. 


H 

Q 

-I 

o 

m 

=> 
I 


a. 
O 

U- 


o 




z „ 









o 


o £ 


* 


o 






..r 1- "J 






IT) 


CC 


u> ^ z 
"J z o 




• 


£ 


< 


I- O N 






z 
o 

o 

-I 

CD 

=> 


z 

UJ 

o 


NORTE COUN 
ARTHQUAKE 
SUBDUCTION 

SCALE 1:100000 


|- 




-I 
< 
(1 


z 
z 


DEL 
EAT E 
ADIA 


1 




n 


z 


Q DC o 
Z (3 ui 






to 


< 

_l 

Q. 


OLDT A 
FOR A 
CA 




: 






1 


I 






© 



O TO 

eE 
If 

TO ■$< 
O Q) 
O . . 



OX) 

II 

CC TO 



CT> C 
TO TO 

£ -- 



III 

ill" 

cc co a> 



° S 

cc o 



' h issl !i| ii 
(i 111 llil 

I SilS. iiis! Ill !ii! 







MATCH 



LINE 




MAT 



C H 



LINE 







o 


< 
o 


LU 

T 












III 


in 


DC 


LU 


7 1 


z 


*" 


< 


K 


o 


N 


O 


Z 
111 


=> 

o 


LU 

< 


Z 

O 


< 

o 


o 


III 





o 



^ o 

u Z 



< □ 

O (0 

<5 




g-8 



8-8 s S. 1 

^ o So 



11 



-s y ~ 
o c c 

£ S Si 

o 
o 
o 
o 





M A T s C H 



LINE 




H 












z S 










tn "j 






O £ 






U- 2 












_l 




o 


Ss : 








- |_ |U 




in 


ec 


CO z 

a | o 

I- ° N 






^ 


< 






Z 
O 


z 
in 


Z UJ _ 


- 




o 

-I 
m 

D 

n 


o 

(0 

o 


DEL NORTE C 
EAT EARTHQU 
1VDIA SUBDUCT 

SCALE 1:100.0 


' 


< 
<i 


z 
z 






LU 

n 


z 


O <T o 

Z O oo 






in 


< 


< < < 








1 


>~ a- ° 








Q. 


_l o 

O "- 




! 




g ■£ 

Z <n 

< S 



<- 










10 

Z 


03 




1- 




E 


S 
in 


< 




_j 


rr 




<) 


- 




IT 


h- 




H 


< 




III 


2 




0. 



© 



§5 



i 



ipli lii 
p 5? pipi it 

iliiifili pi 

iiliiiuEi 8 Pis 

8sS*5p5 8 s; 5533 

rsllgasssil till 




NORTH COAST SCENARIO 



APPENDIX C 



EARTHQUAKE FAULT ZONE MAPS 
FOR THE LITTLE SALMON FAULT 



124° 



PACIFIC 



OCEAN 



42°- 




159 



FIELDS LANDINQ QUADRANGLE 

CALIFORNIA-HUMBOLDT CO. 

IE3 (TOPOORAPHIC) 




MAP EXPLANATION 



Active Fault* 



Faults considered to have been active during Hoiocene lime and to have a 
__£___ relatively high potential lor surface rupture; solid line where accurately located. 

, long dash where approximately located, short dash where inferred, dotted 

where concealed; query (?) indicates additional uncertainty Evidence of histor- 

•■?■- ic offset indicated by year of earthquake -associated event or C 'or displace- 
ment caused by creep or possible creep. 

Special Studies Zone Boundaries 



— O Seaward projection of zone boundary 



STATE OF CALIFORNIA 

SPECIAL STUDIES ZONES 

FIELDS LANDING QUADRANGLE 
OFFICIAL MAP 

Effective: November 1, 1991 



IMPORTANT - PLEASE NOTE 

This map may not show all faults that have the potential for 

Faults shown are the basis lor establishing the boundaries t 
The it 




ha quality of 

4) Fault information on th lS 
investigations (special si 
Public Resources Coda. 



it Chapter 7.5 of Division 2 of tr 



■>j 



State Geologist 



FORTUNA QUADRANOLE 
S (TOPOCRAI 




SCALE 1 2 i COO 



— ■••¥■!>"• '" 



MAP EXPLANATION 



Activ* fault! 



Faults considered to have been active during Holocene time end to have a 
_£_ relatively high potential lor surface rupture, sold line where accurately located. 

. long dash where approximately located, short dash where interred, dotted 

-._- where concealed; query (?) indicates additional uncertainty Evidence of histor- 
■ ■?■■ ic oilset indicated by year of earthquake-associated event or C tor displace- 
ment caused by creep or possible creep 

Spacis! Studies Zone Boundaries 



— O Seaward proiection of zone boundary. 



STATE OF CALIFORNIA 

SPECIAL STUDIES ZON ES 

FORTUNA QUADRANGLE 
OFFICIAL MAP 

Effective: November 1, 1991 




IMPORTANT- PLEASE NOTE 

v a" tauits that have the potential lot surface h 



: Resources Code 



dies) required under Chapter 7 6 of D'v 



State Geologist 



HYDESVILLE QUADRANGLE 



E OF CALIFORNIA-PETE WILSON, GOVERNOR 












. 







Faults considered lo have been aclive during Holocene lime and to have 
_.c.. relatively high poteniial for surface rupluce. solid line whete accutately 

■ long dash where approximately located, shorl dash 

artainty Evidence Of 
d by year ol eenhquake-assooaied event or C lor displ. 
ment caused by creep or possible creep 

Speoni Studies Zone Boundaries 

« These are delmeai 

— O Seaward projection o< zone boundary 



HYDESVILLE QUADRANGLE 
REVISED OFFICIAL MAP 

Effective: November 1, 1991 



IMPORTANT - PLEASE NOTE 



THIS BOOK IS DUE ON THE LAST DATE 
STAMPED BELOW 


BOOKS REQUESTED BY ANOTHER BORROWER 
ARE SUBJECT TO IMMEDIATE RECALL 


F€8 f 9 199? 




RECEIVED 




FEB 1 9 1999 




PSL 




MAR 2 9 1999 




APR 6 1999 
RECEIVED 




APR 5 1939 




PSL 




MAR 1 6 2001 




LIBRARY -UNIVERSITY OF CALIFORNIA, DAVIS 

http://wW:+tfrWcdavis.edu/access/circweb/patron.html 

Automated Phone Renewal (24-hour). (530) 752-1132 

D4613(3/98)M 



PRINTING 

DWR Reprographics 



■n -o 


Or 


3)> 


>i 


25 


So 


> 0) 


H O 


ENARI 
EART 


IO 


o_ 


c z 


Si 


On 


zo 


nr- 


I o 


m-i 


o> 


>S 


w o 


oo 


> m 


o r 


> z 


«o 


c 5 


0J^ 


CO 


oo 


H C 


11 


gs 


zo 


m j> 


r 


Ti 


O 


X 


z 



0) 
"0 

m 
o 

> 

r 

■o 
c 

00 

r 
o 
> 

5 

z 



w 



1,1 |<v '• 



IFOHNIA UAVIS 



3 1175 02029 1970